Embed Size (px)
Citation preview
UNIVERSIDADE FEDERAL DE SANTA MARIA CENTRO DE CIÊNCIAS RURAIS
PROGRAMA DE PÓS-GRADUAÇÃO EM MEDICINA VETERINÁRIA
ATIVIDADE DA ADENOSINA DESAMINASE, CONCENTRAÇÃO DE NUCLEOTIDEOS E NUCLEOSIDEO DE ADENINA EM RATOS
INFECTADOS COM Trypanosoma evansi
TESE DE DOUTORADO
Aleksandro Schafer da Silva
Santa Maria, RS, Brasil
2011
ATIVIDADE DA ADENOSINA DESAMINASE,
CONCENTRAÇÃO DE NUCLEOTIDEOS E
NUCLEOSIDEO DE ADENINA EM RATOS
INFECTADOS COM Trypanosoma evansi
Aleksandro Schafer da Silva
Tese apresentada ao Curso de Doutorado do Programa de Pós-Graduação em Medicina Veterinária, Área de Concentração em
Medicina Veterinária Preventiva, da Universidade Federal de Santa Maria (UFSM, RS), como requisito parcial para obtenção de grau de
Doutor em Medicina Veterinária
Orientadora: Sonia Terezinha dos Anjos Lopes
Santa Maria, RS, Brasil
2011
1
2
Universidade Federal de Santa Maria Centro de Ciências Rurais
Programa de Pós-Graduação em Medicina Veterinária
A Comissão Examinadora, abaixo assinada, aprova a Tese de Doutorado
ATIVIDADE DA ADENOSINA DESAMINASE, CONCENTRAÇÃO DE NUCLEOTIDEOS E NUCLEOSIDEO DE ADENINA EM RATOS
INFECTADOS COM Trypanosoma evansi
Elaborada por Aleksandro Schafer da Silva
como requisito parcial para obtenção do grau de Doutor em Medicina Veterinária
Comissão Examinadora:
Sonia Terezinha dos Anjos Lopes, Dra. (UFSM) (Presidente/Orientadora)
Silvia Gonzalez Monteiro, Dra. (UFSM)
Daniela Bitencourt Rosa Leal, Dra. (UFSM)
Margarete Dulce Bagatini, Dra (UFFS)
Cleci Menezes Moreira, Dra. (UNIPAMPA)
Santa Maria, 09 de dezembro de 2011.
3
AGRADECIMENTOS
A todos da minha família pela compreensão, ajuda, apoio e carinho, em especial, pai,
mãe, vó Auria e minha namorada Rose Carla.
A todos que contribuíram para a realização deste trabalho, fica expresso aqui a minha
gratidão. À Universidade Federal de Santa Maria e ao Programa de Pós-Graduação em
Medicina Veterinária desta instituição pela oportunidade de realização de mais uma etapa na
minha formação. A CAPES pelo apoio financeiro.
Em especial agradeço aos meus orientadores: Sonia Terezinha dos Anjos Lopes, Silvia
Gonzalez Monteiro e Cinthia Melazzo Mazzanti pelos anos dedicados à orientação, amizade e
apoio em todos os momentos necessários.
A toda a equipe do Laboratório de Parasitologia Veterinária e Laboratório de
Patologia Clínica desta universidade, em especial a Márcio e Camila que participaram
diretamente desta pesquisa.
4
RESUMO
Tese de Doutorado Programa de Pós-Graduação em Medicina Veterinária
Universidade Federal de Santa Maria
ATIVIDADE DA ADENOSINA DESAMINASE, CONCENTRAÇÃO DE NUCLEOTIDEOS E NUCLEOSIDEO DE ADENINA EM RATOS
INFECTADOS COM Trypanosoma evansi AUTOR: ALEKSANDRO SCHAFER DA SILVA
ORIENTADORA: SONIA TEREZINHA DOS ANJOS LOPES Santa Maria, 09 de dezembro de 2011
O sistema purinérgico é conhecido por ser uma via de sinalização importante em diversos tecidos. Entre os componentes desse sistema destacamos a adenosina, um modulador do sistema nervoso central, circulatório e imunológico. A concentração de adenosina no hospedeiro é controlada pela enzima adenosina deaminase (ADA), presentes em tecidos, células e fluidos. Em virtude disso, os objetivos deste estudo foram (1) determinar a atividade da ADA no Trypanosoma evansi; (2) avaliar a atividade da ADA no soro, eritrócitos, linfócitos e encéfalo e (3) determinar a concentração de nucleotídeos e nucleosideos no soro e córtex cerebral de ratos infectados com T. evansi. Para um primeiro estudo foram infectados dois camundongos com T. evansi. Quando estes animais apresentavam elevada parasitemia (±108 parasito/µL) foi realizada a coleta de sangue e separação dos flagelados por coluna de DEAE-celulose, a fim realização dos ensaios enzimáticos no parasito. Atividade da ADA nas formas trypomastigotas de T. evansi foi determinada por espectofotometria. Em um segundo estudo foi utilizado 39 ratos, divididos em três grupos: grupo A e B (infectado) e grupo C (C1 e C2/controle). Amostras de sangue e encéfalo foram colhidas nos dias 4 pós-infecção (PI) (grupos A e C1) e 20 PI (grupos B e C2). A partir do sangue total colhido com anticoagulante foram separados os linfócitos e eritrócitos para mensuração da atividade da ADA, já o soro foi obtido de amostras de sangue armazenadas em tubos sem anticoagulante. O encéfalo foi separado em cerebelo, córtex cerebral, hipocampo e estriado para avaliar a atividade da ADA em cada estrutura. Então, observou-se redução da atividade de ADA no soro e eritrócitos em ratos infectados com T. evansi em comparação com não-infectados (P <0,05). A atividade de ADA em linfócitos estava diminuída no dia 4 PI e aumentou no dia 20 PI. Não houve diferença da ADA no cerebelo. No córtex cerebral, no hipocampo e estriado ocorreu redução da atividade da ADA nos dia 4 e 20 PI, respectivamente. Em todas as estruturas do encéfalo foi detectada a presença do parasito por PCR. Em um terceiro estudo foram utilizados 24 ratos, sendo 12 controles negativos e outros 12 infectados com T. evansi. Nos dias 4 (n=6 por grupo) e 20 (n=6 por grupo) foram realizadas as coletas de sangue para obtenção do soro e amostras do córtex cerebral para mensuração dos níveis de ATP, ADP, AMP e adenosina. Neste estudo, foi constatado aumento das concentrações de ATP, AMP e adenosina no encéfalo e soro de ratos infectados com T. evansi nos dois períodos avaliados, com exceção dos níveis de adenosina que reduziram no dia 4 PI. Não houve alteração na concentração de ADP. Portanto, na infecção por T. evansi os componentes do sistema purinérgico pode ser alterados, podendo estar envolvido na resposta imunológica, na anemia e nos sinais neurológicos. Palavras-chave: Trypanosoma evansi, ratos, adenosina, adenosina deaminase.
5
ABSTRACT
Doctoral Thesis Programa de Pós-Graduação em Medicina Veterinária
Universidade Federal de Santa Maria
ACTIVITY OF ADENOSINE DEAMINASE, CONCENTRATION OF A DENINE NUCLEOTIDES AND NUCLEOSIDE IN RATS INFECTED WITH
Trypanosoma evansi AUTHOR: ALEKSANDRO SCHAFER DA SILVA
ADVISER: SONIA TEREZINHA DOS ANJOS LOPES Santa Maria, 09 December 2011
The purinergic system is known to be an important signaling pathway in different tissues. Among the components of this system have adenosine, a modulator of central nervous, circulatory and immune systems. The concentration of adenosine in the host is controlled by the enzyme adenosine deaminase (ADA), present in tissues, cells and fluids. As a result, the objectives of this study were (1) to determine the ADA activity in Trypanosoma evansi, (2) evaluate the activity of ADA in serum, erythrocytes, lymphocytes and brain of infected rats, and (3) determine the concentration of nucleotides and nucleosides in serum and cerebral cortex of rats infected with T. evansi. In the first study two mice were infected with T. evansi. When these animals showed high parasitemia (±108 parasites/uL) was performed with blood collection and separation of trypomastigotes by DEAE-cellulose column for performing the assays. Spectrometry was performed by the biochemical detection of ADA in the form trypomastigotes of T. evansi. In a second study, we used 39 rats divided into three groups: group A and B (infected) and group C (C1 and C2 – control group) Samples of blood and brain samples were collected on day 4 PI (A and C1) and 20 PI (B and C2). From the blood (with anticoagulant) were separated lymphocytes and erythrocytes for measurement of ADA activity, since the serum was obtained from blood samples stored in tubes without anticoagulant. The brain was separated into cerebellum, cerebral cortex, hippocampus and striatum to evaluate the ADA activity in each structure. Decrease of ADA activity in serum and erythrocytes in rats infected with T. evansi when compared not-infected (P<0.05). ADA activity in lymphocytes was decreased at day 4 PI and increased in day 20 PI. There was no difference in ADA activity in the cerebellum. In the cerebral cortex caused a reduction of ADA activity on days 4 and 20 PI. Decrease of ADA activity in hippocampus and striatum in the day 4 and day 20 PI, respectively. In a third study, 24 rats were used, 12 used as a negative control and 12 infected with T. evansi. On day 4 (n = 6 per group) and 20 PI (n = 6 per group) were performed to obtain blood samples of serum and cerebral cortex for analysis. The samples were prepared for quantification of ATP, ADP, AMP and adenosine. This study found increased concentrations of ATP, AMP and adenosine in the brain and serum of rats infected with T. evansi in both periods, except that the levels of adenosine decreased on day 4 PI. The ADP concentration did not change in this study. Therefore, the infection by T. evansi purinergic system components can be changed, may be involved in immune response, in anemia and neurological signs. Keywords: Trypanosoma evansi, rats, adenosine, adenosine deaminase.
6
LISTA DE FIGURAS
Capítulo I
Figura 1 – Formas tripomastigotas de T. evansi em esfregaço sanguíneo de ratos
infectados experimentalmente ............................................................................ 12
Figura 2 – Tipos de receptores de nucleotídeos e nucleosídeos de adenina ........................ 19
Figura 3 – Enzimas envolvidas na degradação extracelular de nucleotídeos e
nucleosídeos de adenina ..................................................................................... 19
Figura 4 – Relação entre o sistema imunológico e purinérgico durante a resposta
inflamatória frente a um patógeno ...................................................................... 20
Figura 5 – Nucleotídeos e nucleosídeos têm participação intensa no SNC, atuando na
neurotransmissão (ATP) e neuromodulação (adenosina) em condições
patológicas ........................................................................................................... 22
Figura 6 – Estrutura tridimensional da ADA. As imagens são formadas apartir de dados
reportados por Wilson et. al. (1991). A imagem a direita apresenta o sitio
ativo no centro da estrutura, e as cadeias laterais polares e não polares estão
representadas em rosa e amarelo respectivamente ............................................. 23
7
LISTA DE ANEXOS
ANEXO 1 – Artigo intitulado “Biochemical detection of adenosine deaminase in
Trypanosoma evansi”, publicado na revista Experimental Parasitology ........ 120
ANEXO 2 – Artigo intitulado “Activity of the enzyme adenosine deaminase in serum,
erythrocytes and lymphocytes of rats infected with Trypanosoma evansi”,
publicado na revista Parasitology ................................................................... 123
ANEXO 3 – Artigo intitulado “Trypanosoma evansi: Adenosine deaminase activity in
the brain of infected rats”, publicado na revista Experimental Parasitology .. 131
8
SUMÁRIO
1 INTRODUÇÃO .................................................................................................................... 09
2 CAPÍTULO I: REVISÃO DE LITERATURA ............... .................................................. 11
2.1 Trypanosoma evansi........................................................................................................... 11
2.2 Sistema purinérgico .......................................................................................................... 18
2.3 Adenosina e adenosina deaminase ................................................................................... 21
3 CAPÍTULO II: MANUSCRITOS ...................................................................................... 25
3.1 Artigo I ............................................................................................................................... 26
3.2 Artigo II ............................................................................................................................. 39
3.3 Artigo III ............................................................................................................................ 63
3.4 Manuscrito I ...................................................................................................................... 83
4 DISCUSSÃO ....................................................................................................................... 102
5 CONCLUSÃO .................................................................................................................... 108
6 REFERÊNCIAS ................................................................................................................. 109
7 ANEXOS ............................................................................................................................. 119
9
1 INTRODUÇÃO
O Trypanosoma evansi é um protozoário digenético da seção salivaria, agente
etiológico da doença conhecida como “Mal das Cadeiras” ou “Surra” em equinos (SILVA et
al., 2002; HERRERA et al., 2004). Apresenta ampla distribuição geográfica, podendo ocorrer
na África, Ásia, América Central e do Sul. Comumente é observado parasitando diversas
espécies de animais domésticos e silvestres (SILVA et al., 2002). Os humanos eram
considerados refratários à infecção por T. evansi (KUBIAK; MOLFI, 1954), entretanto Joshi
et al. (2005) relataram o primeiro caso de infecção pelo parasito em um fazendeiro na Índia e
posteriormente uma investigação sorológica e parasitológica identificou 410 pessoas positivas
para T. evansi em populações de vilarejos na Índia (SHEGOKAR et al., 2006).
Os tripomastigotas presentes nos vasos sanguíneos de vertebrados são adquiridos por
insetos durante a ingestão de sangue contaminado, sendo a transmissão atribuída
principalmente aos tabanídeos (Tabanus sp., Chrysops sp. e Hematopota sp.). Há também a
possibilidade de transmissão por morcegos hematófagos (HOARE, 1972). A doença causada
por este protozoário é caracterizada por rápida perda de peso, graus variáveis de anemia, febre
intermitente, edema dos membros pélvicos e das partes baixas do corpo e fraqueza
progressiva (HERRERA et al., 2004; RODRIGUES et al., 2005).
Algumas pesquisas têm mostrado que ratos são altamente suscetíveis à tripanosomose,
mostrando alterações bioquímicas, hematológicas e patológicas associadas a sinais clínicos
como ataxia, tremores e coma terminal em animais não tratados (MENEZES et al., 2004;
WOLKMER et al., 2009). Em um estudo recente, nosso grupo de pesquisa concluiu que ratos
são um ótimo modelo experimental para estudar T. evansi, pois foi observado que os ratos
infectados agudamente e cronicamente podem manifestar sinais neurológicos e problemas
locomotores como paralisia de membros pélvicos com lesões histológicas (Da Silva et al. in
press) semelhantes aos equinos, principais animais afetados naturalmente. A patogenia das
alterações clínicas não está completamente esclarecida e como o sistema purinérgico é
responsavel por várias funções vitais dos mamíferos consideramos oportuno inverstigar esse
sistema na infecção por T. evansi em ratos.
O sistema purinérgico é conhecido por ser uma via de sinalização importante em
diversos tecidos, desencadeando múltiplos efeitos celulares relacionados à neuromodulação,
as resposta imune e inflamatória, dor, agregação plaquetária, vasodilatação mediada pelo
10
endotélio, proliferação e morte celular. Fazem parte desse sistema os nucleotídeos (ATP, ADP
e AMP) e nucleosídeo (adenosina) extracelulares, receptores para os nucleotídeos (P2X e
P2Y) e nucleosideos (A1, A2a, A2b, A3) extracelulares e ectoenzimas (NTPDase, 5’-
nucleotidase e adenosina deaminase), responsáveis pela regulação dos níveis dessas moléculas
(FRANCO et al., 1997; YEGUTKIN, 2008).
A adenosina age como um modulador do sistema nervoso central (SNC) em
mamíferos, regulando o metabolismo das células e desencadeando uma série de efeitos
fisiológicos que participam na apoptose, na necrose e na proliferação celular. Em condições
patológicas, a adenosina desempenha um papel protetor, modulando a liberação de
neurotransmissores e também atuando como um regulador endógeno da imunidade inata, a
defesa do hospedeiro de lesão tecidual excessiva associada à inflamação (FRANCO et al.,
1997; YEGUTKIN, 2008). A concentração de adenosina extracelular é regulada pela
atividade de um pequeno grupo de enzimas importantes, incluindo a adenosina desaminase
(ADA, EC 3.5.4.4), que catalisa a conversão da adenosina em inosina. Altos níveis dessa
enzima são encontrados no sistema linfóide e SNC, podendo também ser encontrada em
menor quantidade nos eritrócitos. Conforme a literatura, a ADA desempenha um papel
importante na função dos linfócitos e é essencial para o crescimento normal, a diferenciação e
a proliferação de linfócitos T (FRANCO et al., 1997; YEGUTKIN, 2008).
A atividade da ADA pode ser um marcador sensível na infecção e ser utilizada para o
acompanhamento do curso da doença. A atividade da ADA mostra-se elevada no soro de
pacientes com tuberculose, theileriose, malária e leishmaniose visceral (OZCAN et al., 1997;
MELO et al., 2000; KHAMBU et al., 2007; ALTUG et al., 2008), porém a atividade dessa
importante enzima não foi investigada nas tripanossomoses, o que justifica este estudo.
Portanto, os objetivos destes experimentos foram: (1) determinar bioquimicamente a atividade
da enzima ADA no T. evansi; (2) investigar a atividade da ADA no soro, eritrócitos, linfócitos
e encéfalo de ratos infectados experimentalmente com T. evansi; (3) mensurar a concentração
de nucleotídeos e nucleosídeo da adenina no soro e córtex cerebral em ratos infectados
experimentalmente com T. evansi.
2 CAPÍTULO I
REVISÃO DE LITERATURA
2.1 – Trypanosoma evansi
Os tripanossomas são micro-organismos pertencentes ao reino Protozoa, filo
Euglenozoa, subfilo Sarcomastigophora, superclasse Mastigophora, classe Zoomastigophora,
ordem Cinetoplastida, família Trypanosomatidae, gênero Trypanosoma. Os tripanossomas
podem ser distribuídos em duas seções: Salivaria, aqueles transmitidos por picadas de vetores
biológicos e Stercoraria, pela contaminação da pele ou das mucosas do hospedeiro (HOARE,
1972; SILVA et al., 2002). O gênero de Trypanosoma da seção salivaria são altamente
patogênicos para pessoas e animais domésticos e estão distribuídos em quatro subgêneros:
Trypanozoon (T. brucei, T. evansi, T. equiperdum), Nannomonas (T. congolense, T. simiae),
Duttonella (T. vivax) e Pycnomonas (T. suis) (CONNOR; VAN DEN BOSSCHE, 2004).
O Trypanosoma evansi (T. evansi) foi o primeiro tripanossoma patogênico descoberto
em 1880 por Griffith Evans, que encontrou organismos móveis no sangue de cavalos e
camelos doentes (MAUDLIN et al., 2004). É o agente etiológico da doença secularmente
conhecida como “mal das cadeiras” ou “surra” em equinos com ocorrência na África, Índia,
Malásia, Indonésia, China, Rússia, Filipinas, América Central e do Sul (LEVINE, 1973;
SILVA et al., 2002). Este protozoário teve sua origem no continente africano e foi introduzido
nas Américas pelos primeiros colonizadores europeus. Desde então, tem causado numerosos
surtos em equinos, resultando em morte e elevados prejuízos aos pecuaristas (SILVA et al.,
2002). Surtos ou casos isolados de tripanossomose têm sido relatados, há vários anos, em
diversas regiões brasileiras (FRANKE et al., 1994; SILVA et al., 1995; HERRERA et al.,
2004). Na região sul do país, onde até 2005 não havia registro de ocorrência desse flagelado,
o número de casos tem aumentado gradativamente anos após ano (COLPO et al., 2005;
CONRADO et al., 2005; RODRIGUES et al., 2005; FRANCISCATO et al., 2007; ZANETTE
et al., 2008).
O T. evansi tem origem africana como mencionado anteriormente, e trabalhos indicam
que ele surgiu a partir da perda do DNA mitocondrial, ou cinetoplasto, do Trypanosoma
brucei, causador da “doença do sono” em humanos. O cinetoplasto (kDNA) é uma rede de
12
DNA circular com replicação independente adicional ao DNA nuclear. Ele é composto por
maxicírculos e minicírculos, que complementarmente expressam o DNA mitocondrial e RNA
ribossômico. Os maxicírculos expressam proteínas que geralmente são componentes de
complexos respiratórios, mas para que essa expressão ocorra, são necessárias certas inserções
ou deleções que são comandadas por RNAs guias (gRNAs) que são produtos da transcrição
dos minicírculos (Liu et al., 2005). No entanto, este protozoário flagelado é geralmente
monomórfico, tendo um pequeno cinetoplasto subterminal. Porém, existem formas
acinetoplásticas em que o DNA cinetoplástico circular é ausente. Estes exemplares são
encontradas em cepas silvestres como resultados de mutação ou após tratamento com
tripanocidas (aceturato de diminazeno). Formas acinetoplásticas também são relatadas após
longo tempo em cultura in vitro e criopreservação (ZWEYGARTH et al., 1990). As cepas
brasileiras são comprovadamente acinetoplásticas (VENTURA et al., 2000). As formas
encontradas na corrente sanguínea são basicamente lancetadas e o corpo é alongado e
achatado. Um flagelo livre está sempre presente. Há uma membrana ondulante bem
desenvolvida e a extremidade posterior pode ser arredondada ou afilada (Figura 1). Seu
tamanho varia de 15 a 33 µm, com média de 24 µm (HOARE, 1972).
Figura 1 – Formas tripomastigotas de T. evansi em esfregaço sanguíneo de ratos infectados experimentalmente.
13
Nos últimos anos, uma grande variedade de pesquisas bioquímicas e moleculares têm
sido empregadas no campo da tripanossomose, tais como a identificação molecular e análise
filogenética dos tripanossomas (AMER et al., 2011) e a regulação da concentração de cálcio
que é extremamente essencial para a vida destes parasitos (DOCAMPO; MORENO, 1996 ).
Também recentemente foi realizada a detecção da atividade de enzimas como a
acetilcolinesterase em compartimentos subcelulares (MIJARES et al., 2011) e a cisteína
proteinases em T. evansi (YADAV et al., 2011), uma das proteinases liberadas por
tripanossomas vivos e mortos que acarretam imunossupressão no hospedeiro infectado,
contribuindo imensamente na patogênese da doença. O gene de uma selenoproteína exclusiva
de tripanossomatídeos, a selTRYP, foi amplificado do cDNA e parcialmente seqüenciado de
T. evansi, portanto os autores sugerem que este parasito é capazes de utilizar selênio para a
formação de selenoproteínas, capaz de proteger o protozoário dos radicas livres produzidos
pelo hospedeiro (TAVARES et al., 2011). Em Trypanosoma brucei, os autores demonstraram
que a atividade de transporte de purinas é regulada pela captação de nucleosídeos e, em
alguns casos, de hipoxantina (SANCHEZ et al., 2002). A existência de dois sistemas de
transporte distintos de adenosina em T. evansi já foi bem documentada, os quais são
necessários para manter as funções vitais do flagelado (SUSWAM et al., 2001; SUSWAM et
al., 2003). Estas novas descobertas podem auxiliar à elucidar a patogênese do T. evansi, assim
como os mecanismos utilizados pelo parasito para sobreviver no hospedeiro.
O T. evansi causa a tripanossomose em um grande número de animais domésticos e
selvagens, entre eles cavalos, camelos, bovinos, gatos, caprinos, suínos, cães, búfalos,
elefantes, capivaras, quatis, antas, tatus, marsupiais, zebuínos, veados e pequenos roedores
silvestres (LEVINE, 1973; SILVA et al., 2002; ATARHOUCH et al., 2003; HERRERA et al.,
2004). Em 2005, foi relatado o primeiro caso de infecção humana em um fazendeiro na Índia
(JOSHI et al., 2005; SHEGAKAR et al., 2006).
A infecção por T. evansi em humanos não é comum, pois os mesmos possuem em seu
plasma sanguíneo uma apolipoproteína ligada a lipoproteínas de alta densidade que é
considerada um fator tripanolítico, chamado apolipoproteína L-1 (APOL1). A APOL1 entra
no protozoário por endocitose e promove a formação de poros na membrana lisossomal,
induzindo o rompimento destes compartimentos e a morte celular (VANHAME et al., 2003).
Um dos tripanossomatídeos Africanos que causa a “doença do sono” em humanos (T. brucei
rhodesiense) expressa uma proteína que confere resistência a APOL1, conhecida como
proteína associada à resistência ao soro (SRA) (XONG et al., 1998). O T. evansi é
14
normalmente susceptível ao plasma humano, como demonstrado por Hawking (1978) e
também por Otto et al. (2010) para um isolado brasileiro. Uma análise molecular do gene da
APOL1 do paciente indiano demonstrou uma rara mutação nos dois alelos, que levava à
formação de dois stop codons no meio da fase aberta de leitura do gene, impedindo então a
expressão da APOL1 funcional neste paciente, o que provavelmente foi determinante para o
desenvolvimento da infecção (VANHOLLEBEKE et al., 2006).
Tripomastigota é a forma dos tripanossomas presentes nos vasos sanguíneos de
vertebrados, que são disseminados por insetos hematófagos durante o repasto sanguíneo
(SILVA et al., 2002). Como a transmissão é mecânica, não há o desenvolvimento do
hematozoário em nenhum órgão do vetor, e quanto menor a diferença de tempo entre os
repastos sanguíneos, maiores são as possibilidades de passagem do parasita para um novo
hospedeiro (HOARE, 1972). Os principais vetores pertencem aos gêneros Tabanus sp.
(mutucas), porém insetos dos gêneros Stomoxys sp, Haematopota sp. e Lyperosia sp. podem
transmitir o parasita (SILVA et al., 2002). Na América Central e do Sul o morcego
hematófago Desmodus rotundus é considerado um vetor importante, uma vez que os
tripomastigotas multiplicam-se na corrente circulatória destes animais, os quais podem
permanecer infectados por até um mês, atuando como vetor e também como hospedeiro do
protozoário (HOARE, 1972). Ainda, existe a possibilidade de transmissão oral em carnívoros
que se alimentam da carcaça de animais infectados (RAMIREZ et al., 1979). A via oral pode
ser importante na dispersão de infecção de T. evansi em cachorros, quatis e capivaras, que
podem ser infectados em consequência das brigas frequentes entre animais infectados e não
infectados. Além disso, espécies gregárias como coatis e capivaras têm um comportamento
agressivo facilitando a transmissão oral do protozoário entre eles, e mantendo a infecção no
grupo social, já que a forma crônica da doença causada por T. evansi foi identificada em
capivaras (Hydrochaeris hydrochaeris) e quatis (Nasua nasua), possíveis reservatórios do
agente. Os cães e ruminantes também podem atuar como reservatórios do T. evansi quando o
curso da doença for crônico (HERRERA et al., 2004).
A patogenicidade dos tripanossomas no hospedeiro varia de acordo com a cepa do
Trypanosoma sp., a espécie do hospedeiro, fatores não específicos afetando o animal (outras
doenças, estresse, etc.) e condições epizootiológicas locais (HOARE, 1972). Os T. evansi se
reproduzem por fissão binária longitudinal quando estão no sangue de seu hospedeiro (BRUN
et al., 1998). Esta multiplicação inicia-se no local da picada, na pele, invadindo a corrente
sanguínea e o sistema linfático do hospedeiro, levando a picos de febre e induzindo a uma
resposta inflamatória (CONNOR; VAN DEN BOSSCHE, 2004).
15
Os tripanossomatídeos africanos da seção salivaria, a qual pertence o T. evansi,
possuem um interessante mecanismo para evadir as defesas do hospedeiro: as glicoproteínas
variáveis de superfície, ou variant surface glycoproteins (VSGs). Toda a superfície do
protozoário (aproximadamente 95%) é recoberta por VSGs, que possuem a propriedade de se
alterar, “enganando” o sistema imune humoral do hospedeiro (PAYS et al., 2004). O genoma
desses tripanossomatídeos possui centenas de genes que codificam para diferentes VSGs, e
apenas um é expresso por vez. As VSGs são traduzidas com um domínio N- terminal que é
variável e um domínio C-terminal que é altamente conservado e possui uma sequência para
âncoras de GPI (glicofosfatidilinositol) que as sustentam na superfície do parasito. Quando os
protozoários mudam sua cobertura de VSGs ocorrem os picos de parasitemia, observados na
forma crônica da doença (CARRINGTON et al., 1991).
Em infecções naturais e experimentais, observou-se que a tripanossomose por T.
evansi pode apresentar-se com um quadro clínico agudo e crônico. Geralmente, a fase aguda
da infecção é caracterizada pelo surgimento de febre intermitente, edema subcutâneo, anemia
progressiva, cegueira, letargia e alterações hemostáticas. Os animais afetados agudamente
podem morrer dentro de semanas ou poucos meses. No entanto, as infecções crônicas podem
durar anos (BRUN et al., 1998). Durante a fase crônica, ocorre o agravamento dos sinais
clínicos e consequentemente observa-se nos animais infectados caquexia, edema,
incoordenação motora e paralisia de posterior (BRANDÃO et al., 2002; SILVA et al., 2002;
RODRIGUES et al., 2005). Os sinais neurológicos têm sido descritos na fase terminal da
doença, principalmente em equinos, bovinos, veados e búfalos infectados naturalmente
(TUNTASUVAN et al., 1997; TUNTASUVAN; LUCKINS, 1998; TUNTASUVAN et al.,
2003; RODRIGUES et al., 2005).
A principal alteração hematológica identificada em animais com tripanossomose é a
anemia acentuada (CONNOR; VAN DEN BOSSCHE, 2004). A doença é marcada pela
diminuição no valor de hematócrito, na concentração de hemoglobina e no número de
eritrócitos totais. As alterações eritrocitárias podem incluir microesferócitos, acantócitos,
dacriócitos, micrócitos, vacuolização eritrocitária, policromasia, poiquilocitose, adesão
eritrocitária e eritrofagocitose (ANOSA; KANEKO, 1983; SILVA et al., 1995; CONRADO et
al. 2005). Conforme a literatura, o principal mecanismo responsável pela anemia seria a
liberação de hemolisinas e enzimas pelos tripanossomas, que induziram lesões diretamente na
membrana dos eritrócitos, aumentando a fragilidade dos mesmos. A adesão do complexo
antígeno-anticorpo às membranas eritrocitárias e dos componentes do complemento aos
16
eritrócitos também contribui para anemia, pois promove a eritrofagocitose (CONNOR; VAN
DEN BOSSCHE, 2004). Shehu et al. (2006) relataram que a anemia ocorre em consequência
da atividade da neuraminidase, a qual tornaria os glóbulos vermelhos mais propensos à
fagocitose pelo sistema reticuloendotelial. Recentemente, a anemia também foi atribuída à
peroxidação lipídica, pois o aumento de radicais livres acarreta danos à membrana
eritrocitária (WOLKMER et al., 2009).
Os principais componentes da resposta imune à infecção por T. evansi em
camundongos foram estudados por Baral et al. (2007) e Paim et al. (2011a). Segundo os
autores, o fator de necrose tumoral (TNF), que é importante na infecção de outros
tripanossomatídeos, não influencia na parasitemia ou tempo de sobrevivência dos animais. O
interferon-gama (IFN- γ) também não influenciou a parasitemia e o tempo de sobrevivência,
mas os animais sem o gene do IFNγɣ apresentaram maior chance de desenvolver anemia.
Durante a infecção, outras citocinas que são ativadas tais como a interleucina 1 e 6 (PAIM et
al., 2011). Baral et al. (2007) concluíram que o óxido nítrico, produzido pelo hospedeiro
mediante a ação de IFNγ tem efeito supressivo nas células T do hospedeiro, mas esse efeito
não influencia na parasitemia e tempo de sobrevivência dos camundongos. Estes autores
também observaram o papel da IgM no controle da infecção por T. evansi. Os animais foram
capazes de controlar a infecção em seu início, onde haviam altos níveis de IgM e baixos
níveis de IgG. A queda dos níveis de IgM e aumento de IgG coincidiu com a perda do
controle da infecção. Os camundongos deficientes em IgM também não foram capazes de
controlar o primeiro pico de parasitemia. Para confirmar esta teoria, camundongos deficientes
em IgM foram tratados, antes da infecção, com IgM e IgG purificados de animais infectados,
e apenas os que receberam IgM foram capazes de controlar a infecção, demonstrando assim o
papel fundamental da IgM na resposta à tripanossomose por T. evansi.
O diagnóstico presuntivo desta doença em equinos pode ser feito a partir dos sinais
clínicos, que são bastante característicos nesta espécie. Entretanto, o diagnóstico definitivo
somente poderá ser estabelecido através de exames laboratoriais, como a identificação dos
tripomastigotas em esfregaço de sangue corado, podendo-se também visualizar as formas
móveis em uma gota de sangue fresco entre lâmina e lamínula ao microscópio de luz e
inoculação em animais susceptíveis (KUBIAK; MOLFI, 1954). Segundo Tourantier (1993), a
técnica do micro-hematócrito é a mais adequada para diagnóstico em termos de praticidade,
custo e sensibilidade. A técnica de reação em cadeia da polimerase (PCR) é de grande
sensibilidade (VENTURA et al., 2000).
O aceturato de diminazeno é o produto mais comumente usado no controle da
17
tripanossomose dos animais domésticos, pois apresenta maior índice terapêutico que as outras
drogas na maioria das espécies domésticas. Tem atividade contra tripanossomas que são
resistentes a outros medicamentos e apresenta baixa incidência de resistência (PEREGRINE;
MAMMAM, 1993). Em um estudo recente, uma nova terapia com aceturato de diminazeno
apresentou sucesso de 85,7% na cura de gatos infectados com T. evansi (DA SILVA et al.,
2009). Outro produto de eficácia curativa para T. evansi é o suramim, fármaco este utilizado
no humano infectado com o parasito (JOSHI et al., 2006). No entanto, este fármaco tem uma
limitação para animais devido ao elevado custo do tratamento. Em virtude disso, terapias
alternativas com plasma humano (OTTO et al., 2010) devem ser testadas para serem
utilizadas em casos de resistência do protozoário aos quimioterápicos.
Estudos recentes mostraram que um produto análogo da purina, 3-desoxiadenosina
(cordycepin), foi eficaz na cura da infecção por T. brucei em camundongos, tanto na fase
aguda e crônica (com envolvimento do sistema nervoso central) da doença (ROTTENBERG
et al., 2005; VODNALA et al., 2008). Segundo esses autores, a eficácia do tratamento está
relacionado com a proteção do cordycepin contra a enzima adenosina desaminase (ADA), que
é responsável pela desaminação do análogo da adenosina. Portanto, o protocolo de tratamento
exige a combinação de cordycepin com um inibidor da ADA, como deoxycoformycin.
Cordycepin, quando protegido contra desaminação, também possui atividade biológica contra
tripanossomas (ROTTENBERG et al., 2005; VODNALA et al., 2008). Os nucleosídeos do
parasito são alvos de uma via metabólica que torna os tripanosomas vulneráveis, de uma
forma que outras drogas disponíveis não fazem (ROTTENBERG et al., 2005). O metabolismo
das purinas em tripanossomas e outros parasitas representa uma vulnerabilidade específica,
pois tripanossomas, como outros protozoários, não podem participar na síntese de novas
purinas quando o cordycepin liga-se aos recepetores específicos das purinas e portanto esta
incapacidade de tripanossomas em sintetizar novas purinas tem sido explorado como um alvo
terapêutico na tripanossomose (ROTTENBERG et al., 2005; VODNALA et al., 2008). Foi
constatada susceptibilidade de T. evansi ao cordycepin in vitro (100%) e uma eficácia curativa
de 42,5% em ratos infectados, quando administrado combinado ao cordycepin (2 mg/kg) com
EHNA hydrochloride (2 mg/kg), pela via intraperitonial (DA SILVA et al., 2011b).
Pesquisas tem mostrado que ratos são altamente suscetíveis à tripanossomose,
mostrando alterações bioquímicas, hematológicas e patológicas associadas à sinais clínicos
como ataxia, tremores e coma terminal em animais não tratados (MENEZES et al., 2004;
WOLKMER et al., 2009). Em estudo recente, concluiu-se que os ratos são um ótimo modelo
18
experimental para estudar T. evansi, pois foi observado que ratos infectados agudamente e
cronicamente podem manifestar sinais neurológicos e problemas locomotores, como paralisia
de membros pélvicos com lesões histológicas (DA SILVA et al., in press) semelhantes aos
equinos, principais animais afetados naturalmente. Nestes mesmos animais, foi constatado,
uma redução de atividade da enzima Ca2+ ATPase associada à peroxidação lipídica em
músculos do membro pélvico de ratos infectados com T. evansi, fato este que dificulta a saída
de cálcio das células e consequentemente leva à lesão celular (TONIN et al., 2011). O
estresse oxidativo também já foi relatando em roedores parasitados por T. evansi (OMER et
al., 2007; WOLKMER et al., 2009) e associado à patogenia da anemia nesta doença.
Os sinais neurológicos e a resposta inflamatória de ratos infectados com T. evansi
foram correlacionados com as alterações no sistema colinérgico, mais especificamente às
enzimas acetilcolinesterase e butirilcolinesterase, que são responsáveis pela regulação da
aceticolina, um importante neurotransmissor e modulador imunológico (DA SILVA et al.,
2011a; 2011b). Com base nestes resultados, os ratos Wistar foram considerados um bom
modelo experimental para estudos de tripanossomose por T. evansi, e avaliação de sua
influência sobre o sistema purinérgico.
2.2 - Sistema purinérgico
O sistema purinérgico é conhecido por ser uma via de sinalização importante em
diversos tecidos, desencadeando múltiplos efeitos celulares. É considerado um sistema
primitivo, envolvido em muitos mecanismos neurais e não-neurais e em eventos de curta e
longa duração, incluindo a resposta imune e a inflamatória, a dor, a agregação plaquetária, a
vasodilatação mediada pelo endotélio, a proliferação e a morte celular (BURNSTOCK, 2004).
Três componentes principais fazem parte do sistema purinérgico: nucleotídeos e
nucleosídeos extracelulares, seus receptores (Figura 2) e ectoenzimas (Figura 3) responsáveis
pela regulação de níveis destas moléculas (YEGUTKIN, 2008). Os nucleosídeos (inosina e
adenosina) são moléculas resultantes da união de uma base púrica ou pirimídica com uma
pentose (ATKINSON et al., 2006). Os nucleotídeos de adenina como ATP, ADP e AMP são
considerados importantes moléculas sinalizadoras em tecidos (YEGUTKIN, 2008).
19
Figura 2 – Tipos de receptores para nucleotídeos e nucleosídeo de adenina (Fonte: Yegutkin 2008).
Figura 3 – Enzimas envolvidas na degradação extracelular de nucleotídeos e nucleosídeo de adenina (Fonte: Schetinger et al., 2007).
Estudos têm demonstrado que os nucleotídeos e nucleosídeos da adenina regulam
processos relacionados à tromborregulação, modulam a resposta imune e sinalizam vias
20
crucias para o desenvolvimento e funcionamento do sistema nervoso (BURNSTOCK, 2002).
No sistema vascular estas moléculas participam nas funções cardíacas em respostas
vasomotoras e atividade plaquetária, sendo o ADP o principal agonista envolvido no
recrutamento e agregação das plaquetas (ATKINSON et al., 2006). Já o ATP, em altas
concentração, e a adenosina pode atuar inibindo a agregação plaquetária e modulando o tônus
vascular (SOSLAU; YOUNGPRAPAKORN, 1997; ANFOSSI et al., 2002). ATP e a
adenosina também participam na ativação ou inibição do sistema imunológico (Figure 4).
Dependendo da concentração, o ATP tem funções pró-inflamatórias, pois é responsável pela
estimulação e a proliferação de linfócitos, células envolvidas na liberação de citocinas
(BOURS et al., 2006). Enquanto isso, a adenosina apresenta-se como uma molécula
antiinflamatória (GESSI et al., 2007).
Figure 4 – Relação entre o sistema imunológico e purinérgico durante a resposta inflamatória frente a um patógeno (Fonte: Bours et al., 2006)
Todas as funções dos nucleotídeos e nucleosídeo de adenina são mediadas por
receptores purinérgicos presentes na superfície de diferentes tipos de células (YEGUTKIN,
21
2008). Para nucleotídeos existem dois grupos de receptores (P2X e P2Y), sendo o P2X um
receptor acoplado a canais iônicos e P2Y acoplado à proteína G (Figura 2). Os receptores para
adenosina incluem quatro tipos (A1, A2a, A2b, A3), os quais são proteínas transmembrana
acopladas à proteína G (YEGUTKIN, 2008).
O controle dos níveis extracelulares de nucleotídeos e nucleosídeo de adenina são
realizados por enzimas ancoradas na membrana celular ou meio intersticial. Dentre estas
enzimas destacamos as ecto-nucleosídeo trifosfato difosfohidrolase (E-NTPDase), ecto-
nucleotídeo pirofosfatase (E-NPPs), 5’-nucleotidase e adenosina desaminase (ADA)
(YEGUTKIN, 2008). Estas enzimas atuam em conjunto, formando uma cadeia enzimática
que tem início com a ação da E-NTPDase e da E-NPP as quais hidrolisam o ATP e ADP,
formando o AMP, que em seguida é hidrolisado pela 5’-nucleotidase formando adenosina.
Finalmente, a adenosina é desaminada pela ADA em inosina (YEGUTKIN, 2008).
2.3 Adenosina e adenosina desaminase (ADA)
A adenosina, um importante componente do sistema purinérgico e age como um
modulador do SNC (Figure 5). Em mamíferos, regula o metabolismo das células e
desencadeia uma série de efeitos fisiológicos que participam na apoptose, necrose e
proliferação celular. Em condições patológicas, a adenosina desempenha um papel protetor,
modulando a liberação de neurotransmissores e atuando como um regulador endógeno da
imunidade inata, a defesa do hospedeiro de lesão tecidual excessiva associada à inflamação
(RATHBONE et al., 1999; HASKO; CRONSTEIN, 2004; SITKOVSKY; OHTA, 2005;
BURNSTOCK, 2006; DESROSIERS et al., 2007).
A concentração de adenosina extracelular é regulada pela atividade de um pequeno
grupo de enzimas importantes, incluindo a adenosina desaminase (ADA, EC 3.5.4.4 – Figure
6), que catalisa a conversão da adenosina em inosina, seu metabólito inativo. Altos níveis
desta enzima são encontrados no sistema linfóide (linfonodos, baço e timo), podendo também
ser encontrada, mas em menor quantidade, nos eritrócitos (CRISTALLI et al., 2001;
SABOURY et al., 2003). A ADA foi detectada na superfície de muitos tipos celulares,
incluindo sinaptossomas cerebrais. A expressão de atividade desta enzima é heterogênea em
tecidos periféricos e no SNC. A atividade da ADA apresenta uma grande variação em áreas
22
cerebrais de acordo com as vias purinérgicas (GEIGER et al., 1986; FRANCO et al., 1986;
1997). Estudos têm demonstrado que a ADA desempenha um papel importante na função dos
linfócitos e é essencial para a diferenciação e a proliferação de linfócitos T (FRANCO et al.,
1997; CODERO et al., 2001). Na superfície das células hematopoiéticas, pode atuar na
maturação de células vermelhas (ARAN et al., 1991). A deficiência de ADA pode contribuir
para condições patológicas (ALDRICH et al., 2000).
Figura 5 – Os nucleotídeos e nucleosído da adenina têm participação intensa no SNC, atuando como neurotransmissor (ATP) e neuromoduladores (ADA) em condiçoes fisiológicas e/ou patológicas. (Fonte: Schetinger et al., 2007).
Como mencionado anteriormente, a ADA é amplamente distribuída nos tecidos dos
animais vertebrados e divide-se em duas isoformas ADA1 e ADA2. Os tecidos contêm
predominantemente ADA1. Já a ADA2 é o principal componente do soro e é um suposto
estimulador de células-T (FRANCO et al., 1997; BURNSTOCK, 2006).
23
Figura 6 – Estrutura tridimensional da ADA. As imagens são formadas a partir de dados relatados por Wilson et. al. (1991). A imagem a direita apresenta o sítio ativo no centro da estrutura, e as cadeias laterais polares e não polares estão representadas em rosa e amarelo respectivamente (FRANCO et al., 1998).
A ADA1 é uma proteína monômera com uma massa molecular de aproximadamente
40 kDa. A localização da ADA1 é principalmente citosólica, sendo encontrada em todo o
organismo e também na superfície de macrófagos, linfócitos B e em alguns linfócitos T. Esta
pode estar combinada com uma glicoproteína dimérica não específica (CD26) de
aproximadamente 200 kDa, designada proteína combinante (cp) (TSUBOI et al., 1995). O
complexo ADA-proteína combinante constitui uma ecto-ADA, a qual é responsável pelo
controle dos níveis de adenosina extracelulares (SAURA et al., 1996; FRANCO et al., 1997).
Estudos envolvendo a sinalização mediada pela adenosina no SNC demonstraram que além da
interação com CD26, a ADA1 pode atuar como uma ecto-enzima ancorada aos receptores de
adenosina (A1 e A2b), mediando os processos de sinalização deste nucleosídeo
neuromodulador (CIRUELA et al., 1996; ROMANOWSKLA et al., 2007).
A ADA1 e a ADA2 apresentam diferenças, tanto estruturais quanto cinéticas. A massa
molecular da ADA2 é de aproximadamente 100 kDa e representa uma menor parte da
atividade da ADA em tecidos, sendo abundante no plasma (IWAKI-EGAWA et al., 2004). A
fonte celular e a função da ADA2 plasmática ainda não estão completamente esclarecidas
(KOBAYASHI et al., 1993), porém dados recentes têm sugerido que ela pode ser secretada
por monócitos ativados em processos inflamatórios (IWAKI-EGAWA et al., 2006).
A atividade da ADA pode ser um marcador sensível na infecção e ser utilizada para o
acompanhamento do curso na mesma. A atividade da ADA mostra-se elevada no soro de
pacientes com tuberculose, theileriose, malária e leishmaniose visceral (OZCAN et al., 1997;
24
MELO et al., 2000; KHAMBU et al., 2007; ALTUG et al., 2008 ). Apesar da vasta literatura
sobre as alterações induzidas no SNC pelo T. brucei em humanos “doença do sono” e animal
“Nagana” (MAULDIN et al., 2004), o conhecimento das alterações causadas por T. evansi no
SNC dos animais são limitada aos estudos histopatológicos. Portanto, nos propomos a avaliar
o sistema purinérgico na infecção por T. evansi, utilizando como modelo experimental ratos
Wistar.
3 - CAPÍTULO II
ARTIGOS & MANUSCRITO
Os resultados desta tese são apresentados na forma de três artigos e um manuscrito,
com sua formatação de acordo com as orientações das revistas ao quais foram submetidos:
3.1 – ARTIGO I
Biochemical detection of adenosine deaminase in Trypanosoma evansi
Autores: Aleksandro S. Da Silva, Victor C. Pimentel, Jeandre A. S. Jaques, Patrícia Wolkmer,
Kaio C.S. Tavares, Cícera R. Lazzarotto, Luiz C. Miletti, Maria Rosa C. Schetinger, Cinthia
M. Mazzanti, Sonia T.A. Lopes, Silvia G. Monteiro
De acordo com normas para publicação em:
Experimental Parasitology
Artigo publicado na Revista “Experimental Parasitology”
(ANEXO I)
27
Biochemical detection of adenosine deaminase in Trypanosoma evansi
Aleksandro S. Da Silvaa*, Victor C. Pimentelb, Jeandre A. S. Jaquesb, Patrícia Wolkmerb,
Kaio C.S. Tavaresc, Cícera R. Lazzarottoc, Luiz C. Milettic, Maria Rosa C. Schetingerb,
Cinthia M. Mazzantid, Sonia T.A. Lopesd, Silvia G. Monteiroa
a Department of Microbiology and Parasitology, Universidade Federal de Santa Maria, Brazil
b Department of Chemistry, Universidade Federal de Santa Maria, Brazil
c Laboratory of Hemoparasites and Vectors Biochemistry, Universidade do Estado de Santa
Catarina, Lages, Brazil.
d Department of Small Animals, Universidade Federal de Santa Maria, Brazil
*Corresponding author. Tel.: + 55 55 32208958.
E-mail address: [email protected] (A.S. Da Silva)
28
Biochemical detection of adenosine deaminase in Trypanosoma evansi
Abstract
Biochemical and molecular research on parasites has increased considerably in
trypanosomes in the recent years. Many of them have the purpose of identify areas, proteins
and structures of the parasite which are vulnerable and could be used in therapy against the
protozoan. Based on this hypothesis this study aimed to detect biochemically the enzyme
adenosine deaminase (ADA) in Trypanosoma evansi, and to adapt an assay to the
measurement of its activity in trypomastigotes. Firstly, the parasites were separated from the
blood of mice experimentally infected with a DEAE-cellulose column. The ADA activity in
trypomastigotes was evaluated at concentrations of 0.1, 0.2, 0.5, 0.6 and 0.8 mg of protein by
spectrophotometry. ADA activity was observed in the parasites at all concentrations tested
and its activity was proportional to the concentration of protein, ranging between 0.64 and
2.24 U/L in the lowest and highest concentration of protein, respectively. Therefore, it is
possible to detect biochemically ADA in T. evansi, an enzyme that may be associated with
vital functions of the parasite, similar to what occurs in mammals. This knowledge may be
useful in the association of the chemotherapic treatment with specific inhibitors of the
enzyme, in future studies.
Keywords: Trypomastigotes, ADA, adenosine, inosine.
29
1. Introduction
Flagellates of genus Trypanosoma are ubiquitous parasites and infect a wide range of
vertebrate hosts, resulting in immeasurable economic losses (Dobson et al., 2009).
Trypanosoma evansi is the most widely distributed of the pathogenic African animal
trypanosomes, affecting domestic livestock and wildlife in Asia, Africa and Latin America
(Luckins and Dwinger, 2004). The parasite is transmitted mechanically by hematophagous
flies such as Tabanus and Stomoxys spp. and/or vampire bats (Hoare, 1972). The main
affected animals are horses, camels and dogs, but a large number of species may be
parasitized. The animals showed typical clinical signs such as anemia, weight loss and
locomotive disturbance (Hoare, 1972; Maudlin et al., 2004).
T. evansi is classified as monomorphic and is represented by trypomastigotes found in
the bloodstream in the lanced shape, elongated body and flat. The parasite presents free
flagellum, undulating and well developed membrane, the sub-terminal portion kinetoplast or
marginal body and a core (Hoare, 1972; Maudlin et al., 2004). In the recent years, a wide
variety of biochemical and molecular researches have been developed in the field of
trypanosomosis, such as molecular identification and phylogenetic analysis of parasites (Amer
et al., 2011), regulation of calcium concentration (Docampo and Moreno, 1996) and the
detection of enzymes such as acetylcholinesterase in T. evansi (Mijares et al., 2011). In
Trypanosoma brucei, authors demonstrated that purine transport activities are differentially
regulated in the lifecycle stages of parasite, and mediate uptake of purine nucleosides and in
some cases the nucleobase, hypoxanthine (Sanchez et al., 2002). Other researchers reported
the existence of 2 distinct adenosine transport systems in T. evansi (Suswam et al., 2001;
Suswam et al., 2003). According with the authors, this fact is related with the resistance to the
melaminophenyl arsenical drug. These tools help to elucidate the relationships among
30
different species and subspecies and their potency of virulence and pathogenesis (Morrison et
al., 2007).
Recently, our research group reported alterations in the activity of the enzyme
adenosine deaminase (ADA: EC 3.5.4.4) in serum, cells (lymphocytes and erythrocytes) and
brain of rats infected with T. evansi (Da Silva et al., 2011a, Da Silva et al., 2011b). ADA is
considered to be a key enzyme in the purine metabolism, catalyzing the irreversible
deamination of adenosine and deoxyadenosine to inosine and deoxyinosine, respectively, and
closely regulating extracellular adenosine and inosine concentrations in mammals (Franco et
al., 1997). Furthermore, adenosine is a CNS modulator, regulates cell metabolism and triggers
a variety of physiological effects participating in apoptosis, necrosis, cell proliferation, and
modulating the release of the neurotransmitters and tropic factors (Hasko and Cronstein,
2004; Sitkovsky and Ohta, 2005; Desrosiers et al., 2007).
Adenosine and inosine has already been restored in T. evansi and is involved in
various vital functions of the parasite (Suswam et al., 2001; Suswam et al., 2003). In this
study we aimed to investigate the presence of ADA in T. evansi as well as to adapt a
technique to measure the activity of ADA in the parasite.
2. Material and Methods
For this experiment, it was utilized a strain of T. evansi obtained from a naturally
infected dog (Colpo et al., 2005). Isolates were kept in liquid nitrogen according to the
methodology described by Silva et al. (2003). The procedure was approved by the Animal
Welfare Committee of Federal University de Santa Maria (UFSM), number
23081.012513/2009-52.
The trypomastigotes were obtained by inoculation of two mice with 0.2 mL of
cryopreserved blood (Silva et al., 2003) containing 106 parasites per microliter,
31
intraperitoneally. Subsequently, the parasitemia was estimated daily by microscopic
examination of smears. Each slide was mounted with blood collected from the tail vein,
stained by the panoptic method, and visualized by optical microscopy. After the 5th day of
infection the parasitemia was over 100 trypanosomes per microscopic field (1000x). At this
time the animals were anesthetized with isoflurane for blood collection, stored in tubes with
anticoagulant (EDTA 10%).
The volume of 3 mL collected from both mice was eluted with PBS buffer containing
1% glucose (PSG - 1v/v). Thereafter, the separation of trypomastigotes forms by
chromatography was performed on a Poly-Prep® column (Bio-Rad Laboratories, Hercules,
USA) using the DEAE-cellulose resin, according to the technique described by Tavares et al.
(2011). The number of parasites purified was measured by counting in a Neubauer chamber.
In order to concentrate the number of parasites as a pellet, the purified samples (2 mL of PSG
+ parasite) were centrifuged for 30 minutes (14,000 g at 4 C). After the T. evansi (1x109
trypomastigotes per mL) was obtained it was stored in microtubes and kept frozen at -20 ºC
until analyses.
On the day of analysis, the pelleted trypanosomes were resuspended with 50 mmol/L
per mM phosphate buffer, pH 6.5. Then the protein concentration of the trypomastigotes was
measured by the method of Peterson (1977) with bovine serum albumin used as a standard.
The concentration of proteins in the parasite was expressed in mg mL-1.
To measure the ADA activity in the parasites it was adapted the technique used to
evaluate the ADA activity in lymphocytes. ADA activity was measured
spectrophotometrically in trypomastigotes forms of T. evansi by the method of Guisti (1974)
modified. The reaction was started by the addition of the substrate (adenosine) to a final
concentration of 21 mmol/L and incubations were carried out for 1h at 37 °C. The reaction
was stopped by adding 106 mmol/L/0.16 mmol/L phenol-nitroprusside solution. The reaction
32
mixtures were immediately mixed to 125 mmol/L/11 mmol/L alkalinehypochlorite (sodium
hypochlorite) and vortexed. Ammonium sulphate 75 umol/L was used as ammonium
standard. The ammonia concentration is directly proportional to the absorption of indophenol
at 650 nm. The specific activity is reported as U/L. The estimation was performed out in
triplicate and the mean was used for calculation.
3. Results and discussion
In this study, the pelleted trypanosomes eluted with phosphate buffer showed a protein
concentration of 0.86 mg mL-1. The ADA activity was assessed at concentrations of 0, 0.1,
0.2, 0.5, 0.6 and 0.8 mg mL-1. In this study it was detected biochemically the presence of
ADA enzyme in T. evansi. In the lowest and highest concentrations of proteins tested, the
ADA activity was between 0.64 and 2.24 U/L, respectively. Therefore, the ADA activity
increased in proportionately with the concentration of protein used (Fig. 1).
Studies have reported changes in adenosine transport in parasites and ADA activity in
mammals associated with infections by T. brucei, T. evansi, Trypanosoma vivax, Leishmania
donovani and Leishmania infantum (Okochi et al., 1983; De Koning and Jarvis, 1999;
Suswam et al., 2003; Tripathi et al., 2008; Da Silva et al., 2011a,b). However, there is still a
great complexity in the purine transport in trypanosomes. There is the necessity for more
detailed biochemical characterizations of purine transporters in order to provide useful
information for improved drug delivery, and then to achieve a better understanding of drug
resistance phenotypes associated with purine transporters (Suswam et al., 2003). As a result,
this study aimed to investigate the presence of ADA in T. evansi, an enzyme important for
many vital functions in mammals and possibly for the parasites. In the genome of T. brucei it
was identified ADA, which showed similarity among these trypanosomes.
33
The biochemical tests showed ADA activity in T. evansi. Probably, in the parasite this
enzyme is responsible for the regulation of adenosine concentration and consequently inosine,
as occurs in mammals (Franco et al., 1997). In future studies, we aim to investigate the ADA
presence within the parasite using immune markers, as well as the purification and molecular
characterization of the ADA of T. evansi in order to find differences with its counterpart in
vertebrates, which could allow us to propose this enzyme as a potential target for
chemotherapy.
Recent studies showed that the treatment with the adenosine analogue called
cordycepin (3’-deoxyadenosine) when protected by an inhibitor of ADA was effective in the
curative treatment of mice infected with T. brucei (Rottenberg et al., 2005; Vodnala et al.,
2009). The curative effect is obtained because cordycepin binds to receptors, binding site for
nucleosides obtained from the host to vital functions of the parasite. In contrast to most
mammalian cells, trypanosomes cannot synthesize purines de novo. Instead, they depend on
the salvage pathway of nucleosides from the body fluids of the host (Hammond and
Gutteridge, 1984). When used only ADA inhibitor in the treatment of T. brucei in mice,
researchers did not observe curative action and the animals died as a consequence of the
disease (Rottenberg et al., 2005). With the discovery of ADA in the parasite, it becomes
interesting to test in vitro the action of ADA inhibitors on T. evansi, to assess whether the
inhibitor could have some direct harmful effects on the protozoan, by a mechanism that
interferes with vital functions and causes the death of flagellates. This hypothesis will be the
subject of a forthcoming study, together with the characterization of the enzyme in the
parasite, as previously described.
Based on these results, we can conclude that T. evansi has the enzyme adenosine
deaminase, which probably regulates the concentration of adenosine and inosine in the
besieged, as it occurs in mammals. The technique provided demonstrated to be adequate to
34
detect biochemically ADA activity in the parasite. So, this is the first step for the time to come
we can test specific inhibitors of this enzyme in infected animals.
References
Amer, S., Ryu, O., Tada, C., Fukuda, Y., Inoue, N., Nakai, Y., 2011. Molecular identification
and phylogenetic analysis of Trypanosoma evansi from dromedary camels (Camelus
dromedarius) in Egypt, a pilot study. Acta Tropica 117, 39-46.
Colpo, C.B., Monteiro, S.G., Stainki, D.R., 2005. Natural infection by Trypanosoma evansi in
dogs. Ciência Rural 35, 717–719.
Da Silva, A.S., Bellé, L., Bitencourt, P.E.R., Costa, M.M., Oliveira, C.B., Souza, V., Leal,
D.B., Mazzanti, C.M., Lopes, S.T.A., Monteiro, S.G., 2011a. Activity of the enzyme
adenosine deaminase in serum, erythrocytes and lymphocytes of rats infected with
Trypanosoma evansi. Parasitology 138, 201-208.
Da Silva, A.S., Bellé, L., Bitencourt, P.E.R., Perez, H.A., Thomé, G., Costa, M.M., Oliveira,
C.B., Moretto, M.B., Teixeira, M.M.G., Mazzanti, C.M., Lopes, S.T.A., Monteiro, S.G.,
2011b. Trypanosoma evansi: Adenosine deaminase activity in the brain of infected rats.
Experimental Parasitology 108, 173-177.
De Koning, H.P., Jarvis, S.M., 1999. Adenosine transporters in bloodstream forms of
Trypanosoma brucei brucei: substrate recognition motifs and affinity for trypanocidal
drugs. Molecular Pharmacology 56, 1162–1170.
Desrosiers, M.D., Katherine, M.C., Fakir, M.J., Stephens, L.A., Jama, F.M., Shameli, A.,
Mehal, W.Z., Santamaria, P., Shi, Y., 2007. Adenosine deamination sustains dendritic
cell activation in inflammation. Journal of Immunology 179, 1884-1892.
35
Dobson, R.J., Dargantes, A.P., Mercado, R.T., Reid, S.A., 2009. Models for Trypanosoma
evansi (surra), its control and economic impact on small-hold livestock owners in the
Philippines. International Journal Parasitology 39, 1115–1123.
Docampo, R., Moreno, S.N., 1996. The role of Ca2+ in the process of cell invasion by
intracellular parasites. Parasitology Today 12, 61–65.
Franco, R., Casado, V., Ciruela, F., Saura, C., Mallol, J., Canela, E.I., Llouis, C., 1997. Cell
surface adenosine deaminase: much more than an ectoenzyme. Progress Neurobiology
52, 283–294.
Giusti, G. 1974. Adenosine deaminase. In: Bergmeyer, H.U. Methods of Enzymatic Analysis.
Academic Press, New York pp.1092-1099.
Hammond, D.J., Gutteridge, W.E., 1984. Purine and pyrimidine metabolism in the
Trypanosomatidae. Molecular Biochemical Parasitology 13, 243–261.
Hasko, G., Cronstein, B.N., 2004. Adenosine: an endogenous regulator of innate immunity.
Trends Immunology 25, 33-39.
Hoare, C.A., 1972. The Trypanosomes of mammals: a zoological monograph. Oxford,
Blackwell, 749p.
Luckins, A.G., Dwinger, R.H., 2004. Non-tsetse-transmitted animal Trypanosomiasis. In:
Maudlin, I., Holmes, P.H., Miles, M.A. (Eds.). The Trypanosomiases. CABI Publishing,
Wallingford, UK, pp.269–281.
Maudlin, I., Holmes, P., Miles, M.A., 2004. The trypanosomiases. CABI Publishing,
Wallingford. 640p.
Mijares, A., Concepción, J.L., Vielma, J.R., Portillo, R., 2011. Immune detection of
acetylcholinesterase in subcellular compartments of Trypanosoma evansi. Parasitology
Research 108, 1-5.
36
Morrison, L.J., Mc Cormack, G., Sweeney, L., Likeufack, A.C., Truc, P., Turner, C.M., Tait,
A., MacLeod, A., 2007. Use of multiple displacement amplification to increase
thedetection and genotyping of Trypanosoma species samples immobilized on
FTAfilters. American Journal Tropical Medicine and Hygiene 76, 1132–1137.
Okochi, V.I., Abaelu, A.M., Akinrimisi, E.O., 1983. Studies on the mechanism of adenosine
transport in Trypanosoma vivax. Biochemistry International 6, 129-139.
Peterson, G.L., 1977. Simplification of the protein assay method of Lowry et al. which is
more generally applicable. Analytic Biochemistry 83, 346–356.
Rottenberg, M.E., Masocha, W., Ferella, M., Petitto-Assis, F., Goto, H., Kristensson, K.,
McCaffrey, R., Wigzell, H., 2005. Treatment of African trypanosomiasis with
cordycepin and adenosine deaminase inhibitors in a mouse model. Journal Infection
Disease 192, 1658-1665.
Sanchez, M., Tryon, R., Green, J., Boor, I., Landfear, S., 2002. Six related
nucleoside/nucleobase transporters from Trypanosoma brucei exhibit distinct
biochemical functions. Journal Biology Chemistry 277, 21499-21504.
Silva, R.A.M.S., Sanchez, V., Dávila, A.M.R., 2003. Metodologia da criopreservação dos
Trypanosoma evansi e Trypanosoma vivax. Embrapa Pantanal, Corumbá. 3p.
Sitkovsky, M.V., Ohta, A., 2005. The ‘danger’ sensors that STOP the immune response: the
A2 adenosine receptors? Trends Immunology 26, 299-304.
Suswam, E.A., Taylor, D.W., Ross, C.A., Martin, R.J., 2001. Changes in properties of
adenosine transporters in Trypanosoma evansi and modes of selection of resistance to
the melaminophenyl arsenical drug, Mel Cy. Veterinary Parasitology 102, 193–208.
Suswam, E.A., Ross, C.A., Martin, R.J., 2003. Changes in adenosine transport associated with
melaminophenyl arsenical (Mel CY) resistance in Trypanosoma evansi: down-
regulation and affinity changes of the P2 transporter. Parasitology 127, 543–549.
37
Tavares, K.C.S., Da Silva, A.S., Wolkmer, P., Monteiro, S.G., Miletti, L.C., (2011)
Cryopreservation of Trypanosoma evansi after DEAE-cellulose purification: Evaluation
of infective parameters. Research Veterinary Science 90, 257-259.
Tripathi, K., Kumar, R., Bharti, K., Kumar, P., Shrivastav, R., Sundar, S., Pai, K., 2008.
Adenosine deaminase activity in sera of patients with visceral leishmaniasis in India.
Clinica Chimica Acta 388, 135-138.
Vodnala, S.K., Ferella, M., Lundén-Miguel, H., Betha, E., van Reet, N., 2009. Preclinical
Assessment of the Treatment of Second-Stage African Trypanosomiasis with
Cordycepin and Deoxycoformycin. PloS Neglected Tropical Diseases 3, 495.
38
Fig. 1: Biochemical detection of adenosine deaminase activity in trypomastigotes forms of T.
evansi. Relationship between ADA activity and protein concentration of the parasite.
3.2 – ARTIGO II
Activity of the enzyme adenosine deaminase in serum, erythrocytes and lymphocytes of
rats infected with Trypanosoma evansi
Autores: Aleksandro S. da Silva, Luziane P. Bellé, Paula E.R. Bitencourt, Viviane C.G.
Souza, Marcio M. Costa, Camila B. Oliveira, Jeandre A. Jaques, Daniela B.R. Leal, Maria B.
Moretto, Cinthia M. Mazzanti, Sonia T.A. Lopes, Silvia G. Monteiro
De acordo com normas para publicação em:
Parasitology
Artigo publicado na Revista “Parasitology”
(ANEXO II)
40
Activity of the enzyme adenosine deaminase in serum, erythrocytes and lymphocytes of
rats infected with Trypanosoma evansi
Aleksandro S. da Silvaac*, Luziane P. Belléb, Paula E.R. Bitencourtb, Viviane C.G. Souzaa,
Marcio M. Costac, Camila B. Oliveiraa, Jeandre A. Jaques, Daniela B.R. Leala, Maria B.
Morettob, Cinthia M. Mazzantic, Sonia T.A. Lopesc, Silvia G. Monteiroa
a Department of Microbiology and Parasitology, Universidade Federal de Santa Maria, Brazil
b Department of Clinical Analysis and Toxicological, Universidade Federal de Santa Maria,
Brazil
c Department of Small Animals, Universidade Federal de Santa Maria, Brazil
*Corresponding author. Department of Microbiology and Parasitology, Universidade Federal
de Santa Maria, Camobi – 9, Building 20, Room 4232. CEP 97105900. Santa Maria – RS,
Brazil Tel. and Fax: + 55 55 32208958. E-mail [email protected]
41
Activity of the enzyme adenosine deaminase in serum, erythrocytes and lymphocytes of
rats infected with Trypanosoma evansi
Abstract
In Trypanosoma evansi infections are commonly observed changes in hemogram and
the enzyme adenosine deaminase (ADA) plays important roles in the production and
differentiation of blood cells. Thus, this study aim was to evaluate the activity of ADA in
serum, erythrocytes and lymphocytes of rats infected with T. evansi compared not-infected.
Were used 30 adult rats divided into three uniform groups. The animals in groups A and B
were infected with 2 x 106 trypomastigotes/rats, intraperitoneally. Rodents from group C
(control group), were not-infected. Blood collection was performed on days 4 and 20 post-
infection (PI) in order to get an acute and other chronic infection stage of disease. The blood
collected was used to assess the activity of ADA. In the blood, reduced hematocrit and
increased lymphocytes were correlated with ADA activity in erythrocytes and lymphocytes.
We observed reduction of ADA activity in serum and erythrocytes in rats infected with T.
evansi compared to not-infected (P<0.05). ADA activity in lymphocytes was decreased in 4
days, when the parasitemia was high and increased after 20 days, when the number of
circulating parasites was low. In conclusion, our results showed that the ADA activity was
altered in serum, lymphocytes and erythrocytes of rats in experimental infection by T. evansi,
concomitantly with hematological parameters.
Keywords: trypanosomosis, ADA, anemia, lymphocytosis, rats.
42
1. Introduction
Trypanosoma evansi is a digenetic flagellate implicated in the infection of a large
number of domestic and wild animals, such as equines, canines, felines, rabbits, capybaras,
ring-tailed coatis, bovines and buffaloes (Dávila and Silva 2000; Herrera et al. 2004; Tarello
2005; Da Silva et al. 2008) and humans (Joshi et al. 2005). This protozoan is the agent of
trypanosomosis, a disease with broad distribution in Africa, Asia, and Latin America (Lun
and Desser 1995). The trypomastigotes present in blood vessels of vertebrate hosts are
transmitted by blood-sucking insects during feeding. The insect vectors are most commonly
tabanide species (Tabanus sp., Chrysops sp., and Hematopota sp.) and vampire bats (Hoare
1972).
Two features of the disease were reported in Brazil: the acute syndrome, responsible
for the death of equines and non-treated canines, and the chronic syndrome, which affects
many wild animals as Hydrochaeris hydrochaeris and Nasua nasua (Herrera et al. 2004). The
acute form is characterized by intermittent fever, subcutaneous widespread edema,
progressive anemia and blindness. Clinical signs disappear during the subacute phase and the
trypanosomosis may often go undiagnosed during clinical examination. Accurate diagnosis is
only possible during the chronic stage of the disease, where clinical signs are more evident
and the animal’s condition is more severely affected (Silva et al. 2002).
Adenosine deaminase (ADA: EC 3.5.4.4) is considered to be a key enzyme in purine
metabolism, catalyzing the irreversible deamination of adenosine and deoxyadenosine to
inosine and deoxyinosine, respectively, closely regulating extracellular adenosine
concentrations (Franco et al. 1997). Adenosine deaminase activity has been detected on the
surface of hematopoietic cells (Aran et al. 1991). Researchers described a family in which
there is a dominantly inherited form of hemolytic anemia associated with a notable increase of
43
ADA activity in erythrocytes but with normal ADA levels in other blood cells, including
lymphocytes (Valentine et al. 1977).
ADA is present in all cell types, but high ADA activity is present in the thymus,
lymphoid tissues and peripheric lymphocytes. It has been demonstrated that this enzyme plays
an important role in lymphocyte function and is essential for the normal growth,
differentiation and proliferation of T lymphocytes (Franco et al. 1997; Codero et al. 2001).
The observation that ADA deficiency leads to severe combined immunodeficiency syndrome
points to the physiological importance of controlling extracellular adenosine levels in the
immune system (Aldrich et al. 2000).
Anemia by T. evansi is often described and it is characterized by decreased values of
erythrocytes, hemoglobin and hematocrit. However, its causes are not completely understood
(Silva et al. 1995; Aquino et al. 2002). In infections by this protozoan, leukocyte changes are
described as neutropenia, neutrophilia, monocytosis, lymphopenia, lymphocytosis (Silva et al.
1995; Marques et al. 2000; Wolkmer et al. 2009).
Considering the functions of ADA in leukocyte and hematopoietic system, this study
aimed to evaluate the activity of this enzyme in serum, erythrocytes and lymphocytes of rats
infected with T. evansi.
2. Material and methods
A total of 30 adult rats, males, with a mean age of 90 days and weighing in average
300 (±29) grams were used in this study. The animals were kept in cages with 10 animals
each in a room experiment with temperature and humidity controlled (25ºC; 70%). They were
fed with commercial ration and water ad libitum. All animals received a formulation
containing pyrantel pamoate, praziquantel and fenbendazole and were submitted to a period of
44
15 days of adaptation. All animals were apparently healthy when the experimental period
begun (day 0).
These rats were divided into three groups of 10 animals each. The rats in groups A and
B were inoculated intraperitoneally (Day 1) with a strain of T. evansi that had been obtained
from a naturally infected dog (Colpo et al. 2005) and had been kept in liquid nitrogen. The
number of inoculated flagellates was estimated by using a Neubauer chamber (Wolkmer et al.
2007). This study aimed to evaluate the acute and chronic disease in rat, so the infectious dose
used for groups A and B was 2 x 106 trypomastigotes/animal in fresh blood and blood
cryopreserved, respectively (Da Silva et al. 2009a). The collection of samples from animals in
group A was performed on day 4 post-infection (PI) and group B was on day 20 PI. Group C
(negative control) consisted of healthy rats, not infected by T. evansi, but received a
physiological solution by the same way. Group C was divided into two groups (C1 and C2)
and the material was collected on day 4 and 20 PI in order to compare with the infected
groups (A and B). Parasitemia was estimated daily by microscopic examination of smears.
Each slide was mounted with blood collected from the tail vein, stained by the panoptic
method, and visualized at a magnification of 1000x.
The animals were anesthetized in a chamber with isoflurane for collection of blood by
cardiac puncture (8mL). The storage of the samples was considered accordingly to the
analysis. Thus, part of the material collected was allocated in tubes containing anticoagulant
for separation of lymphocytes (4mL), separation of erythrocytes (2mL) and analysis of
hemogram (1mL). The volume of 1mL was stored in a tube without anticoagulant to obtain
serum.
Erythrocytes count, hematocrit (Ht), hemoglobin concentration (Hb), mean
corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC) and total
leukocytes were evaluated. Smears were mounted and stained by the panoptic method. The
45
determination of microhematocrit was performed according to the technique described by
Feldman et al. (2000), and blood smears were stained with panoptic method to perform
differential leukocyte. Erythrocytes count and hemoglobin concentration were determined
using an electronic counter.
Erythrocytes were obtained from whole blood with EDTA, according to the technique
described by Hostetter and Johnson (1989). Erythrocytes were resuspended to hematocrit in
Hepes-buffered at 10%. As the erythrocytes, lymphocytes were also obtained from whole
blood with EDTA by gradient separation using Ficoll-Histopaque™ plus, according to the
technique described by Böyum (1968). The samples stored in tubes without anticoagulant was
centrifuged for 10 minutes, and the serum was obtained. The ADA activity was measured
immediately after obtaining the erythrocytes, lymphocytes and serum.
ADA activity was measured spectrophotometrically in serum, lymphocytes and
erythrocytes by the method of Giusti and Gakis (1971). The reaction was started by addition
of the substrate (adenosine) to a final concentration of 21 mmol/l and incubations were carried
out for 1 h at 37 °C. The reaction was stopped by adding 106 mmol/l/0.16 mmol/l phenol-
nitroprusside/ml solution. The reaction mixtures were immediately mixed to 125 mmol/l/11
mmol/l alkalinehypochlorite (sodium hypochlorite) and vortexed. Ammonium sulphate of 75
umol/l was used as ammonium standard. The ammonia concentration is directly proportional
to the absorption of indophenol at 650 nm. The specific activity is reported as U/L in serum
and lymphocytes and U/g of Hb in erythrocytes.
The data were submitted to one-way analysis of variance (ANOVA) followed by the
Tukey’s test (P<0.05). The effect of ADA in erythrocytes and lymphocytes on hematocrit and
lymphocytes was analyzed by linear regression, respectively. The analyses were performed
using SAS statistical package (SAS Institute, Cary, NC, USA) with a significance level of 5%
(P <0.05).
46
The procedure was approved by the Animal Welfare Committee of Federal University
de Santa Maria (UFSM), number 23081.012513/2009-52, in accordance to Brazilian laws and
ethical principles published by the Colégio Brasileiro de Experimentação Animal (COBEA).
3. Results
Examination of peripheral smear blood showed that the pre patent period in rats
experimentally infected had variation between 24 and 72 hours. The peak of parasitemia at
day 4 PI in group A (63 trypanosomes per microscopic field at 1000 x magnification) and
irregular waves of parasitemia were observed in group B, ranging from zero to three
trypomastigotes per microscopic field (Fig. 1). Seven (7/10) rats in group A showed up
apathetic, slow movements, disorientation and gasping on day 4 PI. In group B, the animals
did not show any clinical change, as well as the not-infected rats (group C).
Hematological changes was observed in the infected rats as the decrease in hematocrit
(Fig. 3a), erythrocyte count and hemoglobin content (Table 1 - P<0.05). The mean of MCV
and the mean of MCHC did not differ among groups, characterizing a normocytic–
normochromic anemia (Table 1). Simultaneously with hematological changes, the rats of
group A showed leukocytosis (Table 1) and lymphocytosis (Fig. 4a), as compared to group B
and C.
The ADA activity in serum was reduced in the groups infected with T. evansi
compared to not-infected rats (P<0.001 – Fig. 2). In erythrocytes, the ADA activity was
reduced on day 4 and 20 (Figure 3b), but was more pronounced in 20 days when the
parasitemia was low (Fig. 1). In the chronic phase it was observed a positive correlation (r2:
0.82) between the ADA activity in erythrocytes and the hematocrit values (P<0.001 – Fig.
3d).
47
In lymphocytes, the activity of ADA was reduced in the acute phase (Day 4), when the
parasitemia was high, but showed an increase of ADA activity in 20 days (Fig. 4b), when the
parasitemia was low (Fig. 1) and the number of lymphocytes was normal (Fig. 4-a). In acute
phase it was observed negative correlation (r2: -0.60) between the ADA activity in
lymphocytes and total number of lymphocytes (P<0.05).
4. Discussion
Many studies have reported changes in adenosine transport and ADA activity
associated with infections by Trypanosoma brucei, Trypanosoma evansi, Trypanosoma vivax,
Leishmania donovani and Leishmania infantum (Okochi et al. 1983; De Koning and Jarvis
1999; Suswam et al. 2003; Tripathi et al. 2008). However, a study that correlates the acute
and chronic effect of experimental infection with T. evansi in the ADA activity in the serum,
erythrocytes and lymphocytes of rats has not been found in the literature.
It has been observed an increased ADA activity in serum samples, erythrocytes,
leukocytes and plasma hemoglobin concentrations with vivax malaria as compare to control
group (Ozcan et al. 1997). Authors described significantly increased ADA activity in visceral
leishmaniasis patients compared to healthy controls (Khambu et al. 2007). Researchers
showed that intraperitoneal injection of the adenosine analogue cordycepin (3´-
deoxyadenosine) for treatment of the encephalitic stage of human African trypanosomosis,
together with an adenosine deaminase inhibitor (coformycin or deoxycoformycin), cures T.
brucei infection in mice (Rottenberg et al. 2005). Therefore, we see how ADA activity may
be associated with trypanosome infection, as in this study with T. evansi that rat had reduced
enzyme activity in blood cells and serum.
In the acute phase of this study we observed a reduction of ADA activity in serum,
erythrocytes and lymphocytes of rats infected with T. evansi compared to healthy rats. At this
48
stage, rats had four days of infection and high parasitemia (Fig. 1). The reduction in ADA
activity would have caused an increase in the extracellular concentrations of adenosine, which
would be converted to inosine. Adenosine acts as a sensor and provides information to the
immune system about the tissue damage or acute inflammatory changes occurring in the
vicinity of the immune system (Kumar and Sharma 2009). The reduction in ADA activity in
lymphocytes, would lead to interaction of adenosine with adenosine receptors that exist in
many cell types, with possible anti-inflammatory effects, among them the inhibition of Th1
immune response. In acute infection caused by T. cruzi there is a predominance of Th1 and
cellular response with production of interferon-γ (Kumar and Tarleton 2001). Therefore,
inhibition of this response by the action of extracellular adenosine in purinergic receptors
could be a compensatory effect, attenuating inflammation and tissue damage. The treatment
of macrophages with interferon-γ up regulates the expression of the adenosine receptor, A2B,
and the activation of A2B receptors is involved with the deactivation of macrophages, possibly
through an increase of cAMP (Xaus et al. 1999). This reinforces the concept of anti-
inflammatory action of adenosine as a way to preserve cells and tissues.
The ADA may be expressed as an ectoenzyme on the surface of lymphocytes. In the
serum there is another isoenzyme, ADA2, which has a low affinity for the substrate (Muraoka
et al. 1990). Thus, it will only increase its activity in higher concentrations of substrate, unlike
the lymphocyte isoform. The concentrations of extracellular adenosine in this study seems to
be sufficient for activation of the enzyme in serum, assuming that they could be binding on
the adenosine receptors in blood cells. Regarding the ADA activity in erythrocytes, reduction
of enzyme activity seems to follow the decrease in total erythrocytes, which could be verified
in future by observing the expression of ectoenzymes the surface of red blood cells.
Researchers mentioned that red blood cells are relatively well supplied with ADA and
circulating damaged erythrocytes release significant amounts of ADA, a process that may
49
predispose to vasoocclusive events (Muraoka et al. 1990). Based on this information, we
hypothesized that ADA activity was increased in serum and/or plasma, in consequence of the
decrease in red blood cells due to a hemolytic process, a cause of anemia in trypanosomosis
(Jackson et al. 1996). However, this was not observed in our study. Therefore, despite the
positive correlation between hematocrit and activity levels in erythrocytes, further studies are
necessary to clear the role of ADA in anemia caused by T. evansi in rats.
In addition, in the chronic phase our experiment showed that the parasitemia had
stabilized and fluctuated between 0 and 3 parasites per field (1000x). At the same time we
find that the ADA activity in serum and erythrocytes was reduced in rats with
trypanosomosis, and in lymphocytes ADA activity was increased when compared to not-
infected. The low parasitemia suggests that the compensatory effect of an anti-inflammatory
like adenosine is no longer necessary. Thus, increased ADA activity in lymphocytes, reducing
the extracellular concentrations of adenosine and favoring an inflammatory response that
would be sufficient to contain the spread of the parasite without major tissue damage. The low
concentration of extracellular adenosine also prevents activation of isoforms present in
erythrocytes and serum, probably due to a low affinity for the substrate.
Researches observed that ADA activity in serum of patients with idiopathic
Parkinson's disease has been recently found significantly higher than in normal controls,
suggesting that high serum ADA activity may be involved in the pathogenesis of Parkinson's
disease through peripheral T-lymphocyte activation (Chiba et al. 1995). Increase in serum
ADA activities in patients with cutaneous leishmaniasis (Ozcan et al. 1998), change in
activity of this enzyme may also be related to pathogenesis of the parasite, as well as in
Parkinson's disease. Rather, this study showed reduced ADA activity in serum of rats infected
with T. evansi, different from what occurred in infection by Leishmania sp. (Ozcan et al.
1998; Khambu et al. 2007).
50
An important aspect to be discussed is that T. evansi caused an acute infection in the
rats, but can also be chronic for some rodents. These protozoa are Salivarian trypanosomes
which are usually more virulent and pathogenic than Stercorarian trypanosomes (Menezes et
al. 2004). The detection of parasitemia in rats (24 h) occurred earlier than previously reported
in experimentally infected rats (Queiroz et al. 2000; Al-Mohammed 2006; Omer et al. 2007),
probably due to the high pathogenicity of this strain. Although authors reported that R.
norvegicus is a suitable model for the study of the parasitemic wave of T. evansi (Queiroz et
al. 2000), the typical undulating course of parasitemia was observed in the group B of this
experiment. According to Da Silva et al. (2009a) the longevity of rats may be related to the
type of inoculum used. When they are made of successive infections in rats, there is an acute
phase with high parasitemia and death of animals within 5 days PI. Now, when the inoculum
used was cryopreserved in liquid nitrogen the longevity of rodents can increase considerably,
resulting in a chronic phase. In rats the disease was characterized by high levels of
parasitemia along with clinical signals of apathy, weakness, ataxia and severe anemia
(Wolkmer et al. 2009), similar to what occurred in the acute phase of this experiment.
Previous studies from our laboratory showed that in the infection with T. evansi
hematological changes are commonly related to other factors, but major changes depend on
the degree of parasitemia and period of infection (Wolkmer et al. 2007; Da Silva et al.
2009b). Our research group has already found in the erythrocytes a decreased activity of
acetylcholinesterase in cats (Da Silva et al. 2010) and an increased lipid peroxidation in rats
(Wolkmer et al. 2009) infected with T. evansi. It is important to state that these alterations
might be related to pathogenesis of the disease or just a consequence of anemia according to
researchers, because adenosine is related to maturation of erythrocytes (Franco et al. 1990;
Jackson et al. 1996). This question also persists for the decreased ADA activity in
erythrocytes in this study.
51
Based on these results, we conclude that the parasitism by T. evansi alters the activity
of ADA in serum, erythrocytes and lymphocytes of rats experimentally infected, suggesting
that trypanosomiasis can interfere with a purinergic signaling. Other studies should be
performed to verify the expression of ectoenzymes in the surface of red blood cells and
lymphocytes in trypanosomiasis, in order to understand the relationship of the ADA with
anemia and lymphocytosis in this disease.
References
Aldrich, M., Blackburn, M. and Kellems, R. (2000). The importance of adenosine
deaminase for lymphocyte development and function. Biochemical and Biophysical
Research Communications 272, 311-335.
Al-Mohammed, H. I. (2006). Parasitological and immunological response of experimental
infection with Trypanosoma evansi in rats. Journal of the Egyptian Society of
Parasitology 36, 363–371.
Aquino, L. P. C. T., Machado, R. Z., Alessi, A. C., Marques, L. C., Castro, M. B. and
Malheiros, E. B. (2002). Aspectos hematológicos, bioquímicos e anatomopatológicos da
infecção de Trypanosoma evansi em cães. Arquivo Brasileiro de Medicina Veterinária e
Zootecnia 54, 8-18.
Aran, J. M., Colomer, D., Matutes, E., Vives-Corrons, J. L. and Franco, R. (1991).
Presence of adenosine deaminase on the surface of mononuclear cells: immunochemical
localization using light and electron microscopy. Journal of Histochemistry &
Cytochemistry 39, 1001-1008.
Böyum, A. (1968). Isolation of mononuclear cells and granulocytes from human blood.
Isolation of mononuclear cells by one centrifugation, and of granulocytes by combining
52
centrifugation and sedimentation at 1 g. Scandinavian journal of clinical and laboratory
investigation. Supplementum 97, 77–89.
Chiba, S., Matsumoto, H., Saitoh, M., Kasahara, M., Matsuya, M. and Kashiwagi, M.
(1995). A correlation study between serum adenosine deaminase activities and peripheral
lymphocyte subsets in Parkinson's disease. Journal of Neurology Science 132, 170-173.
Codero, O., Salgado, F., Fernández-Alonso, C., Herrera, C., Lluis, C., Franco, R. and
Nogueira, M. (2001). Cytokines regulate membrane adenosine deaminase on human
activated lymphocytes. Journal of leukocyte biology 70, 920–930.
Colpo, C. B., Monteiro, S. G. and Stainki, D. R. (2005). Natural infection by Trypanosoma
evansi in dogs. Ciencia Rural 35, 717-719.
Da Silva, A. S., Costa, M. M., Lopes, S. T. A. and Monteiro, S. G. (2008). Alterações
hematológicas em coelhos infectados experimentalmente pelo Trypanosoma evansi.
Ciência Rural 38, 538–542.
Da Silva, A. S., Wolkmer, P., Gressler, L. T., Otto, M. A., Bess, F., Tavares, K. C.,
Zanette, R. A. and Monteiro, S. G. (2009a). Patogenicidade do isolado de Trypanosoma
evansi em ratos inoculados com o parasito em sangue in natura e criopreservado. Ciência
Rural 39,1842-1846.
Da Silva, A.S., Zanette, R. A., Wolkmer, P., Costa, M. M., Gressler, L. T., Faccio, L.,
Santurio, J. M., Lopes, S. T. A. and Monteiro, S. G. (2009b). Trypanosoma evansi:
hematologic changes in experimentally infected cats. Experimental Parasitology 123, 31-
34.
Da Silva, A. S., Spanevello, R., Stefanello, N., Wolkmer, P., Costa, M. M., Zanette, R. A.,
Lopes, S. T. A., Santurio, J. M., Schetinger, M. R. C. and Monteiro, S. G. (2010).
Influence of Trypanosoma evansi in blood, plasma, and brain cholinesterase of
experimentally infected cats. Research Veterinary Science 88, 281-284.
53
Dávila, A. M. R. and Silva, R. A. M. S. (2000). Animal trypanosomiasis in South America.
Current status, partnership, and information technology. Annals of the New York Academy
of Sciences 916, 199-212.
De Koning, H. P. and Jarvis, S. M. (1999). Adenosine transportersin bloodstream forms of
Trypanosoma brucei brucei: substrate recognition motifs and affinity for trypanocidal
drugs. Molecular and Pharmacology 56, 1162-1170.
Franco, R., Aran, J.M., Colomer, D., Matutes, E., Vivis-Corrons, J.L. (1990). Association
of adenosine deaminase with erythrocyte and platelet plasma membrane: an
immunological study using light and electron microscopy. The Journal of Histochemistry
and Cytocheinistry 38, 653-658.
Franco, R., Casado, V., Ciruela, F., Saura, C., Mallo, J., Canela, E. I. and Llouis, C.
(1997). Cell surface adenosine deaminase: much more than an ectoenzyme. Progress in
Neurobiology 52, 283-294.
Feldman, B. V., Zinkl, J. G. and Jain, N. C. (2000). Schalm’s Veterinary Hematology.
Lippincott Williams & Wilkins, Philadelphia. 1344pp.
Giusti, G. and Gakis, C. (1971). Temperature conversion factors, activation energy, relative
substrate specificity and optimum pH of adenosine deaminase from human serum and
tissues. Enzyme 12, 417-425.
Herrera, H. M., Davila, A. M., Norek, A., Abreu, U. G., Souza, S. S., Andrea, O. S. and
Jansen, A. M. (2004). Enzootiology of Trypanosoma evansi in Pantanal, Brazil.
Veterinary Parasitology 125, 263-275.
Hoare, C. A. (1972). The Trypanosomes of mammals: a zoological monograph. Oxford,
Blackwell, 749pp.
54
Hostetter, M. K. and Johnson, G. M. (1989). The erythrocyte as investigator of
inflammation. Generation of amidated C3 by erythrocyte adenosine deaminase. Journal of
Clinical Investigation 84, 665-671.
Jackson, E. K., Mi, Z., Koehler, M.T., Carcillo, J.A. and Herzer, W.A. (1996) Injured
erythrocytes release adenosine deaminase into the circulation. Journal of Pharmacology
and Experimental Therapeuties 279, 1250–1260.
Joshi, P. P., Shegokar, V. R., Power, R. M, Herder, S., Katti, R., Salkar, H. R., Dani, V.
S. and Bhargava, A. (2005). Human Trypanosomosis caused by Trypanosoma evansi in
India: the first case report. American Journal of Tropical Medicine and Hygiene 73, 491–
495.
Lun, Z.R. and Desser, S. S. (1995). Is the broad range of hosts and geographical distribuition
of Trypanosoma evansi attributable to the loss of maxicircle kinetoplast DNA?
Parasitology Today 11, 131–133.
Khambu, B., Mehta, K. D., Rijal, S., Lamsal, M., Majhi, S. and Baral, N. (2007). Serum
nitrite level and adenosine deaminase activity is altered in visceral Leishmaniasis. Nepal
Medical College Journal 9, 40-43.
Kumar, S. and Tarleton, R. L. (2001). Antigen-Specific Th1 But Not Th2 Cells Provide
Protection from Lethal Trypanosoma cruzi Infection in Mice. Journal of Immunology
166, 4596-4603.
Kumar, V. and Sharma, A. (2009). Adenosine: an endogenous modulator of innate immune
system with therapeutic potential. European Journal of Pharmacology 616, 7-15.
Marques, L. C., Machado, R. Z., Alessi, A. C., Aquino, L. P. C. T. and Pereira, G. T.
(2000). Experimental infection with Trypanosoma evansi in horses: clinical and
haematological observations. Revista Brasileira de Parasitologia Veterinária 9, 11-15.
Menezes, V. T., Queiroz, A. O., Gomes, M. A., Marques, M. A. and Jansen, A. M. (2004).
55
Trypanosoma evansi in inbred and Swiss–Webster mice: distinct aspects of pathogenesis.
Parasitology Research 94, 193–200.
Muraoka, T., Katsuramaki, T., Shiraishi, H. and Yokoyama, M. M. (1990). Automated
enzymatic measurements of adenosine deaminase isozymes activities in serum. Analytical
Biochemistry 187, 278-282.
Okochi, V. I., Abaelu, A. M. and Akinrimisi, E. O. (1983). Studies on the mechanism of
adenosine transport in Trypanosoma vivax. Biochemistry International 6, 129-139.
Omer, O. H., Mousa, H. M. and Al-Wabel, N. (2007). Study on the antioxidant status of
rats experimentally infected with Trypanosoma evansi. Veterinary Parasitology 145, 142–
145.
Ozcan, E., Abdurrahim, K., Salih, G. M., Vedat, B., Adnan, S. and Yuksel, O. (1998).
Adenosine deaminase activities in sera, lymphocytes and granulocytes in patients with
cutaneous leishmaniasis. Memórias do Instituto Oswaldo Cruz 93, 491-494.
Ozcan, E., Abdurrahim, K., Adnan, S., Senel, A. and Necmeddin, A. (1997). Serum
erythrocyte and leukocyte adenosine deaminase activities in patients with vivax malaria in
Turkey. Journal of the Egyptian Society of Parasitology 27, 445–454.
Queiroz, A. O., Cabello, P. H., Jansen, A. M. (2000). Biological and biochemical
characterization of isolates of Trypanosoma evansi from Pantanal of Matogrosso – Brazil.
Veterinary Parasitology 92, 107–118.
Rottenberg, M. E., Masocha, W., Ferella, M., Petitto-Assis, F., Goto, H., Kristensson, K.,
McCaffrey, R. and Wigzell, H. (2005). Treatment of African trypanosomiasis with
cordycepin and adenosine deaminase inhibitors in a mouse model. Journal of Infection
Disease 192, 1658-1665.
56
Silva, R. A. M. S., Herrera, H. M., Domingos, L. B. S., Ximenes, F. A. and Dávila, A. M.
R. (1995). Pathogenesis of Trypanosoma evansi infection in dogs and horses:
hematological and clinical aspects. Ciência Rural 25, 233-238.
Silva, R. A. M. S., Seidl, A., Ramirez, L. and Dávila, A. M. R. (2002). Trypanosoma evansi
e Trypanosoma vivax: biologia, diagnóstico e controle. Corumbá, Embrapa Pantanal.
141pp.
Suswam, E. A., Ross, C. A. and Martin, R. J. (2003). Changes in adenosine transport
associated with melaminophenyl arsenical (Mel CY) resistance in Trypanosoma evansi:
down-regulation and affinity changes of the P2 transporter. Parasitology 127, 543–549.
Tarello, W. (2005). Trypanosoma evansi infection in three cats. Revue Medecine Veterinaire
156, 133-134.
Tripathi, K., Kumar, R., Bharti, K., Kumar, P., Shr ivastav, R., Sundar, S. and Pai, K.
(2008). Adenosine deaminase activity in sera of patients with visceral leishmaniasis in
India. Clinica Chimica Acta 388, 135-138.
Valentine, W. N., Paglia, D. E., lkrtaglia, A. P. and Gilsanz, F. (1977). Hereditary
hemolytic anemia with increased adenosine deaminase (45-70 fold) and decreased
adenosine tniphosphate. Science 195, 783.
Xaus, J., Valledor, A. F., Card, M., Marques, L., Beleta, J., Palacois, J. M. and Celada,
A. (1999). Adenosine inhibits macrophage colony-stimulating factor-dependent
proliferation of macrophages through the induction of p27 kip-1 expression. Journal of
Immunology 163, 4140-4149.
Wolkmer, P., Da Silva, A. S., Carnelutti, J. F., Costa, M. M., Traesel, C., Lopes, S. T. A.
and Monteiro, S. G. (2007). Resposta eritropoética de ratos em diferentes de graus de
parasitemia por Trypanosoma evansi. Ciência Rural 37, 1682-1687.
57
Wolkmer, P., Da Silva, A. S., Carnelutti, J. F., Paim, F. C., Traesel, C., Lopes, S. T. A.
and Monteiro, S. G. (2009). Lipid peroxidation associated with anemia in rats
experimentally infected with Trypanosoma evansi. Veterinary Parasitology 165, 41-46.
58
Table 1: Means and standard deviation of the hematological parameters of rats experimentally
infected with T. evansi.
Parameters Group*
A: Infected (Day 4) B: Infected (Day 20) C: Not-infected
Total erythrocytes (x106/µl) 6.15b (±0.46) 6.34b (±0.65) 7.0a (±0.24)
Hemoglobin (g/dl) 11.8b (±0.46) 12.5b (±0.46) 14.0a (±0.46)
MCV (fl) 62.6a (±2.10) 62.4a (±1.74) 61.0a (±2.40)
MCHC (%) 30.8a (±0.90) 32.6a (±1.10) 31.3a (±0.80)
Total leukocytes (x103/µl) 12.71a (±3.10) 5.27b (±1.2) 5.75b (±0.9)
* Means in the same line followed by different letters are statistically different among them
by Tukey’s test at 5% probability.
59
Fig. 1: Parasitemia of T. evansi in infected rats at day 20 post-inoculation. The collection of
material was performed in groups A and B on day 4 and 20 post-infection when high and low
parasitemia, respectively.
60
Fig. 2: Means and standard deviation of the adenosine deaminase activity in serum of rats
infected whit Trypanosoma evansi (Day 4 and 20 PI) compared to not-infected (n=10).
(*p<0.05)
61
Fig. 3: Means and standard deviation of the hematocrit (a) and adenosine deaminase activity
in erythrocytes (b) of rats infected whit Trypanosoma evansi (Day 4 and 20 PI) compared not-
infected (n=10). Linear regression analysis of individual infected rat hematocrit with
adenosine deaminase activity in erythrocytes of the acute phase (c) and chronic phase (d).
(*p<0.05)
62
Fig. 4: Means and standard deviation of the lymphocytes (a) and adenosine deaminase activity
in lymphocytes (b) of rats infected with Trypanosoma evansi (Day 4 and 20 PI) compared to
not-infected (n=10). Linear regression analysis of individual infected rat number of
lymphocytes with adenosine deaminase activity in lymphocytes of the acute phase (c) and
chronic phase 20 (d). (*p<0.05)
3.3 – ARTIGO III
Trypanosoma evansi: Adenosine deaminase activity in the brain of infected rats
Autores: Aleksandro S. Da Silva, Luziane P. Bellé, Paula E.R. Bitencourt, Herakles A. Garcia
Perez, Gustavo R. Thomé, Marcio M. Costa, Camila B. Oliveira, Marta M. G. Teixeira, Maria
B. Moretto, Cinthia M. Mazzanti, Sonia T.A. Lopes, Silvia G. Monteiro
De acordo com normas para publicação em:
Experimental Parasitology
Artigo publicado na Revista “Experimental Parasitology”
(ANEXO III)
64
Trypanosoma evansi: Adenosine deaminase activity in the brain of infected rats
Aleksandro S. Da Silvaa*, Luziane P. Belléb, Paula E.R. Bitencourtb, Herakles A. Garcia
Perezc, Gustavo R. Thoméb, Marcio M. Costad, Camila B. Oliveiraa, Marta M. G. Teixeirac,
Maria B. Morettob, Cinthia M. Mazzantid, Sonia T.A. Lopesd, Silvia G. Monteiroa
a Department of Microbiology and Parasitology, Universidade Federal de Santa Maria, Brazil
b Department of Clinical Analysis and Toxicology, Universidade Federal de Santa Maria,
Brazil
c Department of Parasitology, Universidade de São Paulo, Brazil
d Department of Small Animals, Universidade Federal de Santa Maria, Brazil
* Corresponding author. Address: Departamento de Microbiologia e Parasitologia da UFSM.
Faixa de Camobi - Km 9, Campus Universitário, 97105-900, Prédio 20, Sala 4232, Santa
Maria – RS, Brasil. Fax: +55 55 3220 8958.
E-mail address: [email protected] (A.S. Da Silva).
65
Trypanosoma evansi: Adenosine deaminase activity in the brain of infected rats
Abstract
The study was undertaken to evaluate changes in the activity of adenosine deaminase
(ADA) in brains of rats infected by Trypanosoma evansi. Each rat was intraperitoneally
infected with 106 trypomastigotes either suspended in fresh (Group A; n=13) and
cryopreserved blood (Group B; n=13). Thirteen animals were used as control (Group C).
ADA activity was estimated in the cerebellum, cerebral cortex, striatum and hippocampus. No
differences (P > 0.05) in ADA activity were observed in the cerebellum between infected and
non-infected animals. Significant (P < 0.05) reductions in ADA activity occurred in cerebral
cortex in acutely (day 4 post-infection; PI) and chronically (day 20 PI) infected rats. ADA
activity was significantly (P < 0.05) decreased in the hippocampus in acutely infected rats, but
significantly (P < 0.05) increased in the chronically infected rats. Significant (P < 0.05)
reductions in ADA activity occurred in the striatum of chronically infected rats. Parasites
could be found in peripheral blood and brain tissue through microscopic examination and
PCR assay, respectively, in acutely and chronically infected rats. The reduction of ADA
activity in the brain was associated with high levels of parasitemia and anemia in acute
infections. Alterations in ADA activity of the brain in T. evansi-infected rats may have
implications for pathogenesis of the disease.
Keywords: Trypanosoma evansi, adenosine deaminase activity, adenosine, brain, rats.
1. Introduction
Trypanosoma evansi and T. brucei are closely phylogenetically related trypanosomes
of African origin (Brun et al., 1998; Lai et al., 2008). T. evansi is the only mechanically
66
transmitted by biting flies and displays the broadest host range and geographical distribution
among all pathogenic trypanosomes, infecting domestic and wild mammals in Africa, Asia
and Latin America (Brun et al., 1998; Ventura et al., 2002; Herrera et al., 2005).
The infection caused by T. evansi in horses develops in two stages, the early, or
haemolymphatic stage, when the parasites multiply and spread in the blood and lymph nodes,
followed by the late or encephalitic stage, when the parasites cross the blood–brain barrier to
invade the central nervous system (CNS). T. evansi causes a devastating horse disease, called
‘‘mal de cadeiras’’ or “surra”, characterized by anemia, immunosuppression, emaciation,
severe neurological signs, motor incoordination, paralysis of hind limbs and death of
untreated animals (Rodrigues et al., 2009; Berlin et al., 2009).
Clinical signs of neurological disorders are reported in horses, camels, buffaloes,
cattle, deer and cats infected by T. evansi (Tuntasuvan et al., 1997; Tuntasuvan et al., 2000;
Rodrigues et al., 2005; Berlin et al., 2009; Da Silva et al., 2010). Brain lesions were reported
in bovines and equines (Tuntasuvan et al., 1997; Rodrigues et al., 2009). Rats are highly
susceptible to the disease, showing hematological, biochemical and pathological changes
associated with ataxia, tremors and terminal coma of untreated animals (Menezes et al., 2004;
Wolkmer et al., 2009). Human infection by T. evansi was reported for the first time in 2005 in
an Indian farmer that showed signs of sensory deficit, disorientation and violent behavior
(Joshi et al., 2005).
Adenosine acts as a CNS modulator in mammals, regulates cell metabolism and
triggers a variety of physiological effects participating in apoptosis, necrosis and cell
proliferation. Under pathological conditions, adenosine plays a protective role by modulating
the release of the neurotransmitters and tropic factors. Adenosine also acts as an endogenous
regulator of innate immunity, protecting the host from excessive tissue injury associated with
67
strong inflammation (Rathbone et al., 1999; Beraudi et al., 2003; Hasko and Cronstein, 2004;
Sitkovsky and Ohta, 2005; Burnstock, 2006; Desrosiers et al., 2007).
The concentration of extracellular adenosine is regulated by the activity of a small
group of important enzymes including adenosine deaminase (ADA; EC 3.5.4.4), which
catalyses the conversion of the adenosine into its inactive metabolite inosine. ADA activity is
widely distributed in tissues and fluids from vertebrate animals in isoforms of ADA1 and
ADA2. Tissue extracts contain predominantly ADA1, which is supposed to be derived mainly
from injured tissues. ADA2 is found in serum and derived from stimulated T-cells. ADA has
been detected on the surface of many cell types, including brain synaptosomes. A
heterogeneous expression of ADA activity can be found among peripheral tissues and even
within the CNS, where high activities of ADA were reported in discrete and diverse brain
areas (Geiger et al., 1986; Franco et al., 1986, 1997).
ADA activities may be sensitive markers for infection severity and for monitoring the
course of infections. The activity of ADA was elevated in the serum of hosts with
tuberculosis, theileriosis, malaria and visceral leishmaniasis (Ozcan et al., 1997; Melo et al.,
2000; Khambu et al., 2007; Altug et al., 2008). No study has demonstrated a relationship of T.
evansi infection with ADA activity in the CNS. Thus, the purpose of the present investigation
was to determine whether T. evansi infection induces changes in ADA activity in the brain
tissues of adult rats.
2. Material and methods
2.1. Experimental animals
Thirty nine adult outbreed male rats (mean age of 90 days) weighing 300 ± 18 g
were maintaining in cages in a room with controlled temperature (25ºC) and humidity (70%).
They were fed (commercial ration) and water ad libitum. Before the experiment, they were
68
treated with pyrantel pamoate, praziquantel and fenbendazole, and submitted to an adaptation
period of 15 days. The procedure was approved by the Animal Welfare Committee of
Universidade Federal de Santa Maria (UFSM), number 23081.012513/2009-52, in accordance
to Brazilian laws and ethical principles of the Colégio Brasileiro de Experimentação Animal
(COBEA).
2.2. Experimental design and trypanosome infection
The rats were divided in three groups of 13 animals each. Animals in groups A and B
were inoculated intraperitoneally (day 0) with a strain of T. evansi that had been obtained
from a naturally infected dog (Colpo et al., 2005) and had been maintaining in liquid nitrogen.
The infective dose (estimated using a hemocytometer) for each animal was 106
trypomastigotes in either fresh (Group A; 0.1 ml) and cryopreserved blood (Group B; 0.2 ml)
in order to elicit acute and chronic infections, respectively (Da Silva et al., 2009). The
collection of blood samples and brains from animals in group A was performed at day 4 post-
infection (PI) while samples for group B were collected at day 20 PI. Group C consisted of 13
healthy non-infected control rats. This group was divided into groups C1 and C2 and blood
samples and brains were collected on days 4 (C1) and 20 (C2) PI for comparison with the
infected groups A and B.
2.3. Estimation of parasitemia
The presence and degree of parasitemia were determined daily for each animal by
blood film examination. A drop of blood was collected from the tail and placed on a slide, and
a thin blood smear was prepared manually (Da Silva et al., 2006). The blood films were
Romanovsky stained and then examined under a microscope, counting 10 fields at 1000x
magnification.
69
2.4. Collection of samples
The animals were anesthetized in a chamber with isoflurane before collection of blood
by cardiac puncture. Thereafter, animals were decapitated following recommendations of the
Ethics Committee and brains of 10 rats from each group were carefully removed avoiding
contamination with peripheral blood, and dissected to separate cerebellum, cerebral cortex,
striatum and hippocampus. Each part of the brain was weighed, homogenized in 10 volumes
of 50 mmol/l per mM phosphate buffer (pH 7.0) and centrifuged for 30 min at 14,000 × g at 4
oC. The supernatant was then collected as described by Bellé et al. (2009).
2.5. Hematologic Parameters
Erythrocyte count, hemoglobin concentration and total leukocyte count were
determined using an electronic counter (CC-550-Celm, São Paulo, Brazil).
2.6. ADA activity in brain
ADA activities were estimated spectrophotometrically (Hitachi U-2800A -
spectrophotometer) by the method of Giusti (1974), which is based on the direct measurement
of the formation of ammonia produced when the enzyme acts on adenosine. Brain
homogenate of cerebral cortex (15mg/mL protein), cerebellum (10mg/mL protein), striatum
(3mg/mL protein) or hippocampus (3mg/mL protein) was added to 21mM of adenosine in 50
mM sodium phosphate buffer (pH 6.5) and incubated at 37 °C for 1 h. The reaction was
stopped by adding 1.5 ml of 106/0.16 mM phenol–nitroprusside solution, which was
immediately mixed with 1.5 ml of 125/11 mM alkaline-hypochlorite (sodium hypochlorite).
The ammonia released would react with alkaline hypochlorite and phenol in the presence of a
catalyst-sodium nitroprusside to produce indophenol (a blue color) and the concentration of
70
ammonia is directly proportional to the absorbance of indophenol read at 620 nm. Ammonium
sulphate of 75µM was used as ammonium standard.
Protein concentration of the brain homogenate was measured by the method of
Peterson (1977) with bovine serum albumin used as a standard. The value of ADA activity in
the brain tissue was expressed as U/mg of protein. The estimation was performed out in
triplicate and the mean was used for calculation.
2.7. DNA extraction and PCR detection of T. evansi in brains of rats
Three rats from each infected group (A and B) and controls (C1 and C2) were
randomly selected to investigate the presence of T. evansi DNA in their brains by PCR. For
this assay, cerebellum, cerebral cortex, striatum and hippocampus, removed using one sterile
blade for each structure from each animal, was individually transferred to sterile tubes
containing 0.5mL ethanol.
For preparation of DNA templates, a small section (0.4 x 0.4 mm) of each brain were
removed, transferred to sterile tubes and washed three times (5 min. each) in bi-distillated
water under shaker. Then, the tissues were cut in small segments, incubated with lysis buffer
(1% SDS, 100 mM EDTA pH 8.0, 20 mM Tris-HCl, pH 8.0, and 350 mg/ml of proteinase K),
at 37ºC for 18 h, centrifuged at 14,000 g for 5 min, and DNA purified using Wizard
Purification Systems (Promega, USA). Purified DNA samples were used as templates for
PCR amplifications of a spliced leader gene sequence using primers and reaction conditions
previously described (Ventura et al., 2002). Amplified DNA fragments were resolved in 2%
agarose gel, stained with ethidium bromide and visualized under U.V. light.
2.8. Statistical analysis
71
The data were summarized means and standard deviations analyzed by ANOVA
followed by the Tukey’s post-test (P < 0.05).
3. Results
3.1. Parasitemia, hematological parameters and clinical signs
Examination of the peripheral blood smears showed a prepatent period between 1-3
days PI. No difference in prepatent period between group A and B. The peak of parasitemia
occurred on day 4 PI in group A (63 trypomastigotes per microscopic field), and irregular
waves of parasitemia (0-3 trypomastigotes per microscopic field) were observed in group B
(Figure 1). Decreased (P < 0.05) levels of erythrocyte count and hemoglobin were observed in
rats of groups A and B, when compared to group C. Animals from group A showed a
significant (P < 0.05) increase in the number of total leukocytes (Figure 2). Seven (7/10) rats
of group A presented apathy, lethargy, disorientation and gasping at day 4 PI. Animals from
group B did not show any clinical sign.
3.2. ADA activity in brain
No difference in ADA activity was detected in the cerebellum between infected and
non-infected animals. A significant (P < 0.05) decrease occurred in cerebral cortex of acutely
and chronically infected animals. In acutely infected rats, the activity was significantly (P <
0.05) reduced in hippocampus, but no alteration was observed in striatum. However, in
chronically infected rats, ADA activity increased significantly (P < 0.05) in the hippocampus
with a concomitant reduction (P < 0.05) in the striatum (Figure 3).
3.3. Detection of T. evansi in brain of rats using PCR assay
72
The PCR assays detected T. evansi DNA in brain parts of acutely and chronically
infected rats. Tissue samples of control animals were all negative for the parasite. The PCR
did not allow for parasite count and the intensity of amplified band could not be quantified.
4. Discussion
Variations in ADA activity occurred in brains of rats during infection by T. evansi,
with respect to components of the brain (cerebral cortex, striatum and hippocampus) and
severity of the disease (acute or chronic infection). Acutely infected animals with high levels
of parasitemia showed neurological disturbances, but chronically infected ones with low
parasitemia had no neurological signs.
The reduction in ADA activity in some brain regions (cerebral cortex, striatum and
hippocampus) may have increased of adenosine levels in the brain. Adenosine plays an
important regulatory role in neuronal activity and has neuroprotective actions in P1
purinoreceptor-mediated pathological conditions (Cunha and Ribeiro, 2000; Cunha, 2001). In
addition, reduction in ADA activity could also contribute to limit inflammation and
subsequent cellular damage (Abbracchio and Ceruti, 2007). Adenosine protects host cells
from excessive tissue injury associated with strong inflammation, existing evidence that
elevated level of this nucleoside potently down-regulates the activation of lymphocytes during
inflammation, playing a regulatory role on dendritic cell immune responses (Desrosiers et al.,
2007). Increased ADA in chronic infected animals may increase the severity of the lesion,
because a decrease in brain adenosine can lead to damage of brain tissue.
Our evidence of different ADA activities among the regions of the brain corroborated
with spatial activity of the enzyme, which correlates with mRNA expressions (Mackiewicz et
al., 2000). Thus, ADA activity may play an important role in the mechanisms that control
regional concentrations of adenosine in the brain, and the differences observed are likely to
73
have important physiological consequences. In experimentally infected horses, the severity of
encephalomyelitis varied in different parts of the brain (Lemos et al., 2008).
Changes in ADA activities were associated with the presence of parasites in peripheral
blood and brain, anemia and neurological signs. These data suggest that the presence of
parasites may be primarily responsible for the reduced ADA activity in the brains of T.
evansi-acutely infected rats (highly parasitemic). Based on our previous studies, rats that
develop the acute infection invariable develop severe hematological and neurological
disorders and died (Wolkmer et al., 2009). The neurological disturbances in T. evansi-infected
hosts could be related to changes in ADA activity in the brains especially in the cerebral
cortex and hippocampus (Mesulam et al., 2002).
In contrast to most mammalian cells, trypanosomatids are unable to engage in de novo
purine synthesis and depend on the salvage pathway of nucleosides from their mammalian
hosts. Studies have been done to identify targets for purine pathway inhibitors of Leishmania
spp., T. brucei, T. vivax and T. evansi (Ogbunude and Ikediobi, 1983; De Koning et al., 1999;
Suswam et al., 2003; Witola et al., 2004; Carter et al., 2008). Although some enzymes of
purine salvage were detected in the bloodstream forms of T. brucei, T. congolense and T.
vivax, homogenates of these trypanosomes apparently lacked adenosine deaminase
(Ogbunude and Ikediobi, 1983). T. brucei and T. cruzi genomes include genes encoding
putative ADA-like enzymes, but to date these enzymes have not been expressed nor was their
function analyzed, as well as not disclosed by the first broad proteomic analysis of T. evansi
(Roy et al., 2010).
In conclusion, T. evansi infection resulted in either the reduction or increase in the
ADA activity in brain of rat. The alterations in ADA activity in the brain of infected rats may
have implications for pathogenesis and neurological signs of the disease.
74
References
Abbracchio, M.P., Ceruti, S., 2007. P1 receptors and cytokine secretion. Purinergic Signal 3,
315–325.
Altug, N., Yüksek, N., Agaoglu, Z.T., Keles, I., 2008. Determination of adenosine deaminase
activity in cattle naturally infected with Theileria annulata. Tropical Animal Health
Production 40, 449-456.
Bellé, L.P., De Bona, K.S., Abdalla, F.H., Pimentel, V.C., Pigatto, A.S., Moretto, M.B., 2009.
Comparative evaluation of adenosine deaminase activity in cerebral cortex and
hippocampus of young and adult rats: effect of garlic extract (Allium sativum L.) on
their susceptibility to heavy metal exposure. Basic & Clinical Pharmacology &
Toxicology 104, 408-413.
Berlin, D., Loeb, E., Baneth, G., 2009. Disseminated central nervous system disease caused
by Trypanosoma evansi in a horse. Veterinary Parasitology 161, 316-319.
Beraudi, A., Traversa, U., Villani, L., Sekino, Y., Nagy, J.I., Poli, A., 2003. Distribution and
expression of A1 adenosine receptors, adenosine deaminase and adenosine deaminase-
binding protein (CD26) in goldfish brain. Neurochemistry International 42, 455–463.
Brun, R., Hecker, H., Lun, Z.R., 1998. Trypanosoma evansi and T. equiperdum: distribution,
biology, treatment and phylogenetic relationship (a review). Veterinary Parasitology 79,
95-107.
Burnstock, G., 2006. Purinergic signaling – an overview. Novartis Found Symposium 276,
26–48.
Carter, N.S., Yates, P., Arendt, C.S., Boitz, J.M., Ullman, B., 2008. Purine and pyrimidine
metabolism in Leishmania. Advance Experimental Medicine Biology 625, 141-154.
Colpo, C.B., Monteiro, S.G., Stainki, D.R., 2005. Natural infection by Trypanosoma evansi in
dogs. Ciencia Rural 35, 717–719.
75
Cunha, R.A., Ribeiro, J.A., 2000. ATP as presynaptic modulator. Life Science 68, 119–137.
Cunha, R.A., 2001. Adenosine as a neuromodulator and as homeostatic regulator in the
nervous system: different role, different sources and different receptors. Neurochemistry
International 38, 107–125.
Da Silva, A.S., Doyle, R.L., Monteiro, S.G., 2006. Método de contenção e confecção de
esfregaço sanguíneo para pesquisa de hemoparasitas em ratos e camundongos.
Faculdade de Zootecnia, Veterinária e Agronomia 13, 83-87.
Da Silva, A.S., Wolkmer, P., Gressler, L.T., Otto, M.A., Bess, F., Tavares, K.C., Zanette,
R.A., Monteiro, S.G., 2009. Patogenicidade do isolado de Trypanosoma evansi em ratos
inoculados com o parasito em sangue in natura e criopreservado. Ciência Rural 39,
1842-1846.
Da Silva, A.S., Zanette, R.A., Wolkmer, P., Costa, M.M., Oliveira, C.B., Soares, C.D.M.,
Santurio, J.M., Lopes, S.T.A., Monteiro, S.G., 2010. Clinical aspects of cats
experimentally infected with Trypanosoma evansi. Comparative Clinical Pathology 19,
85-89.
De Koning, H.P., Jarvis, S.M., 1999. Adenosine transporters in bloodstream forms of
Trypanosoma brucei brucei: substrate recognition motifs and affinity for trypanocidal
drugs. Molecular and Pharmacology 56, 1162–1170.
Desrosiers, M.D., Katherine, M.C., Fakir, M.J., Stephens, L.A., Jama, F.M., Shameli, A.,
Mehal, W.Z., Santamaria, P., Shi, Y., 2007. Adenosine deamination sustains dendritic
cell activation in inflammation. Journal of Immunology 179, 1884-1892.
Franco, R., Canela, E.I., Bozal, J., 1986. Heterogeneous localization of some purine enzymes
in subcellular fractions of rat brain and cerebellum. Neurochemical Research 11, 423–
435.
Franco, R., Casado, V., Ciruela, F., Saura, C., Mallol, J., Canela, E.I., Llouis, C., 1997. Cell
76
surface adenosine deaminase: much more than an ectoenzyme. Progress of
Neurobiology 52, 283–294.
Greiger, J.D., Nagy, J.I., 1986. Distribution of adenosine deaminase activity in rat brain and
spinal cord. Journal of Neuroscience 6, 2707-2714.
Giusti, G., 1974. Adenosine deaminase. In: Bergmeyer, H.U. Methods of Enzymatic Analysis.
Academic Press, New York, pp.1092-1099.
Hasko, G., Cronstein, B.N., 2004. Adenosine: an endogenous regulator of innate immunity.
Trends Immunology 25, 33-39.
Herrera, H.M., Norek, A., Freitas, T.P.T., Rademaker, V., Fernandes, O., Jansen, N.M., 2005.
Domestic and wild mammals infection by Trypanosoma evansi in a pristine area of the
Brazilian Pantanal region. Parasitology Research 96, 121–126.
Joshi, P.P., Shegokar, V.R., Power, R.M., Herder, S., Katti, R., Salkar, H.R., Dani, V.S.,
Bhargava, A., 2005. Human Trypanosomosis caused by Trypanosoma evansi in India:
the first case report. American of Journal Tropical Medicine and Hygiene 73, 491–495.
Khambu, B., Mehta, K.D., Rijal, S., Lamsal, M., Majhi, S., Baral, N., 2007. Serum nitrite
level and adenosine deaminase activity is altered in visceral Leishmaniasis. Nepal
Medical College journal 9, 40–43.
Lai, D.H., Hashimi, H., Lun, Z.R., Ayala, F.J., Lukes, J., 2008. Adaptations of Trypanosoma
brucei to gradual loss of kinetoplast DNA: Trypanosoma equiperdum and Trypanosoma
evansi are petite mutants of T. brucei. Proceedings of the National Academy of
Sciences 105, 1999-2004.
Lemos, K.R., Marques, L.C., Aquino, L.P., Alessi, A.C., Zacarias, R.Z., 2008. Astrocytic and
microglial response and histopathological changes in the brain of horses with
experimental chronic Trypanosoma evansi infection. Revista do Instituto de Medicina
Tropical de São Paulo 50, 243-249.
77
Mackiewicz, M., Geiger, J.D., Pack, A.I., 2000. Simultaneous assessment of ecto- and
cytosolic-5′-nucleotidase activities in brain micropunches. Journal Neuroscience
Methods 104, 9–18.
Mesulam, M.M., Guillozet, A., Shaw, P., Levey, A., Duysen, E.G., Lockridge, O., 2002.
Acetylcholinesterase knockouts establish central cholinergic pathways and can use
butyrylcholinesterase to hydrolyze acetylcholine. Neuroscience 110, 627-639.
Melo, F.A.F., Afiune, J.B., Santos, M.L., Castelo Filho, A., 2000. Diagnóstico da tuberculose
pleural pela ADA, isolada ou combinada a outras variáveis, inclusive em HIV-positivos.
Folha Médica 119, 9-21.
Menezes, V.T., Queiroz, A.O., Gomes, M.A., Marques, M.A., Jansen, A.M., 2004.
Trypanosoma evansi in inbred and Swiss–Webster mice: distinct aspects of
pathogenesis. Parasitology Research 94, 193–200.
Ogbunude, P.O.J., Ikediobi, C.O., 1983. Comparative aspects of purine metabolism in some
African trypanosomes. Molecular & Biochemical Parasitology 9, 279–287.
Ozcan, E., Abdurrahim, K., Adnan, S., Senel, A., Necmeddin, A., 1997. Serum erythrocyte
and leukocyte adenosine deaminase activities in patients with vivax malaria in Turkey.
Journal of the Egyptian Society of Parasitology 27, 445–454.
Peterson, G.L., 1977. Simplification of the protein assay method of Lowry et al. which is
more generally applicable. Analytical Biochemistry 83, 346–356.
Rathbone, M.P., Middlemiss, P.J., Gysbers, J.W., Andrew, C., Herman, M.A.R., Reed, J.K.,
Ciccarelii, R., Di Iorio, P., Caciagli, F., 1999. Trophic effects of purines in neurons and
glial cells. Progress Neurobiology 59, 663–690.
Rodrigues, A., Fighera, R.A., Souza, T.M., Schild, A.L., Soares, M.P., Milano, J., Barros,
C.S.L., 2005. Outbreaks of trypanosomiasis in horses by Trypanosoma evansi in the
state of Rio Grande do Sul, Brazil: epidemiological, clinical, hematological, and
78
pathological aspects. Pesquisa Veterinária Brasileira 25, 239–249.
Rodrigues, A., Fighera, R.A., Souza, T.M., Schild, A.L., Barros, C.S., 2009. Neuropathology
of naturally occurring Trypanosoma evansi infection in horses. Veterinary Pathology
46, 251-258.
Roy, N., Nageshan, R.K., Pallavi, R., Chakravarthy, H., Chandran, S., 2010. Proteomics of
Trypanosoma evansi infection in rodents. PLoS ONE 5, 9796.
Sitkovsky, M.V., Ohta, A., 2005. The ‘danger’ sensors that STOP the immune response: the
A2 adenosine receptors? Trends Immunology 26, 299-304.
Suswam, E.A., Ross, C.A., Martin, R.J., 2003. Changes in adenosine transport associated with
melaminophenyl arsenical (Mel CY) resistance in Trypanosoma evansi: down-
regulation and affinity changes of the P2 transporter. Parasitology 127, 543–549.
Tuntasuvan, D., Sarataphan, N., Nishikawa, H., 1997. Cerebral trypanosomiasis in native
cattle. Veterinary Parasitology 73, 357–363.
Tuntasuvan, D., Mimapan, S., Sarataphan, N., Trongwongsa, L., Intraraksa, R., Luckins,
A.G., 2000. Detection of Trypanosoma evansi in brains of the naturally infected hog
deer by immunohistochemistry. Veterinary Parasitology 87, 223–230.
Ventura, R.M., Takeda, G.F., Silva, R.A.M.S., Nunes, V.L.B., Buck, G.A., Teixeira, M.M.G.,
2002. Genetic relatedness among Trypanosoma evansi stocks by random amplification
of polymorphic DNA and evaluation of a synapomorphic DNA fragment for species-
specific diagnosis. International of Journal Parasitology 32, 53–63.
Witola, W.H., Inoue, N., Ohashi, K., Onuma, M., 2004. RNA-interference silencing of the
adenosine transporter-1 gene in Trypanosoma evansi confers resistance to diminazene
aceturate. Experimental Parasitology 107, 47-57.
Wolkmer, P., Da Silva, A.S., Traesel, C.K., Paim, F.C., Cargnelutti, J.F., Pagnocelli, M.,
Picada, M.E., Monteiro, S.G., Lopes, S.T.A., 2009. Lipid peroxidation associated with
79
anemia in rats experimentally infected with Trypanosoma evansi. Veterinary
Parasitology 165, 41-46.
80
0
10
20
30
40
50
60
70
0 1 2 3 4 6 8 10 12 14 16 18 20
Days post-infection
Try
po
ma
stig
ote
s /
field
(1
00
0x)
..
A: Day 4
B: Day 20
Figure 1: Parasitemia of T. evansi-infected rats with acute or chronic infections.
81
Figure 2: Total erythrocytes, hemoglobin concentration and total leukocytes
of T. evansi- infected (days 4 and 20 post-infection) and non-infected rats.
______________________* *
3
4
5
6
7
8
9
Acute phase (Day 4) Chronic phase (Day 20)
x 106
/µl
Total erythrocytes
______________________* *
10
11
12
13
14
15
16
Acute phase (Day 4) Chronic phase (Day 20)
g/d
l
Hemoglobin
___________*
0
3
6
9
12
15
18
Acute phase (Day 4) Chronic phase (Day 20)
x103
/µl
Total leukocytes
Infected Group Control group
82
Figure 3: Adenosine deaminase activity in cerebellum, cerebral cortex, striatum and
hippocampus of T. evansi-infected (days 4 and 20 post-infection) and non-infected rats.
Cerebel lum
0
0,5
1
1,5
2
2,5
Acute phase (Day 4) Chronic phase (Day 20)
Ad
en
osi
ne
de
am
ina
se a
ctiv
ity(U
/mg
of
pro
tein
)
Cerebral cortex
__________ __________* *
0
0,3
0,6
0,9
1,2
1,5
Acute phase (Day 4) Chronic phase (Day 20)
Ad
en
osi
ne
de
am
ina
se a
ctiv
ity(U
/mg
o
f p
rote
in)
Striatum
_________*
0
1
2
3
4
5
6
Acute phase (Day 4) Chronic phase (Day 20)
Ad
en
osi
ne
de
amin
ase
act
ivity
(U/m
g o
f p
rote
in)
Hippocampus
__________
__________
*
*
0
1
2
3
4
5
6
Acute phase (Day 4) Chronic phase (Day 20)
Ad
en
osi
ne
dea
min
ase
act
ivity
(U
/mg
of
pro
tein
)
Infected Non-infected
83
3.4 – MANUSCRITO I
Influence of Trypanosoma evansi in adenine nucleotides and nucleoside concentration in
serum and cerebral cortex of infected rats
Autores: Aleksandro S. Da Silva, Camila B. Oliveira, Luciana D. Rosa, Claudio A.M. Leal,
Ritiel S. Cruz, Gustavo R. Thomé, Margarete L. Athaíde, Maria R.C. Schetinger, Cinthia M.
Mazzantti, Sonia T.A. Lopes, Silvia G. Monteiro
De acordo com normas para publicação em:
Experimental Parasitology
Artigo submetido à Revista “Experimental Parasitology”
84
Influence of Trypanosoma evansi in adenine nucleotides and nucleoside concentration in
serum and cerebral cortex of infected rats
Aleksandro S. Da Silvaa*, Camila B. Oliveiraa, Luciana D. Rosa, Claudio A.M. Lealb, Ritiel
C. Da Cruzc, Gustavo R. Thoméb, Margarete L. Athaydec, Maria R.C. Schetingerb, Silvia G.
Monteiroa, Sonia T.A. Lopesd
a Department of Microbiology and Parasitology, Universidade Federal de Santa Maria, Brazil
b Department of Chemistry, Universidade Federal de Santa Maria, Brazil
c Department of Industrial Pharmacy, Federal University of Santa Maria, Brazil
d Department of Small Animals, Universidade Federal de Santa Maria, Brazil
*Corresponding author. Department of Microbiology and Parasitology, Universidade Federal
de Santa Maria, Camobi – 9, Building 20, Room 4232. CEP 97105900. Santa Maria – RS,
Brazil Tel. and Fax: + 55 55 32208958. E-mail [email protected]
85
Abstract
This study aimed to evaluate the adenine nucleotides and nucleoside concentration in
serum and cerebral cortex of rats infected with Trypanosma evansi. Each rat was
intraperitoneally infected with 1x106 trypomastigotes suspended in cryopreserved blood
(Group A; n=18). Twelve animals were used as controls (Group B). The infected animals
were monitored daily by blood smears. At days 4 and 20 post-infection (PI) it was collected
serum and cerebral cortex to measure the levels of ATP, ADP, AMP and adenosine by high
performance liquid chromatography (HPLC). In serum there was a significant (P<0.05)
increase in the ATP, AMP and adenosine concentrations at days 4 and 20 PI in infected rats
when compared to not-infected. Furthermore, in the cerebral cortex it was observed a
significant (P<0.05) increase in the concentrations of ATP, AMP and decreased adenosine
levels at day 4 PI. At day 20 PI it was only observed an increase in the AMP and adenosine
concentrations in brain of infected rats when compared to not-infected. It was not observed
any difference in ADP concentration in serum and brain at days 4 and 20 PI. No change was
observed histologically in the cerebral cortex of infected animals. The results allow us to
conclude that infection with T. evansi in rats causes an increase in the concentrations of ATP,
AMP and adenosine in serum and cerebral cortex. These alterations occurred as a result of T.
evansi pathogenesis which involves neurotransmission, neuromodulation and immune
response impairment, as discussed in the manuscript.
Keywords: trypanosomosis, ATP, ADP, AMP, adenosine.
86
1. Introduction
Trypanosoma evansi is a digenetic flagellate implicated in the infection of a large
number of domestic and wild animals (Dávila and Silva, 2000; Silva et al., 2002; Herrera et
al., 2004) and rarely humans (Joshi et al., 2005). This parasite is the agent of trypanosomosis,
a disease with broad distribution in Africa, Asia, and Latin America (Lun and Desser, 1995)
and recently in Europe (Gutierrez et al., 2010). The trypomastigotes present in blood vessels
of vertebrate hosts are transmitted by blood-sucking insects during feeding (Hoare, 1972).
T. evansi causes a devastating mammals disease characterized by anemia,
thrombocytopenia, immunosuppression, emaciation, severe neurological signs, motor
incoordination, paralysis of hind limbs and death of untreated animals (Silva et al. 2002;
Berlin et al., 2009; Rodrigues et al., 2009). Rats (Menezes et al., 2004; Wolkmer et al., 2009;
Tochetto et al. 2010) and horses (Berlin et al. 2009; Rodrigues et al. 2009) are highly
susceptible to this disease, showing hematological, biochemical and pathological changes
associated with ataxia, tremors, terminal coma and paralysis of hind limbs when untreated.
According to the literature, locomotor clinical signs can be associated with inflammatory
infiltrates, meningoencephalitis, edema, necrosis and demyelination in equines (Lemos et al.,
2008; Rodrigues et al., 2009). In a recent study of our research group it has been suggested
that changes in the activity of purinergic system (Da Silva et al., 2011a; 2011b; Oliveira et al.,
2011a; 2011b) and cholinergic system enzymes (Da Silva et al., 2011c) could be involved in
the pathogenesis of trypanosomiasis and exacerbate the clinical signs, hematological and
inflammatory responses caused by T. evansi.
The purinergic system (consisting of enzymes, nucleotides, nucleosides and receptors)
is involved in the regulation of several vital functions of mammals (Gödeche, 2008). The
nucleotides ATP, ADP, AMP and the nucleoside adenosine are secreted by hematological and
endothelial cells and used as mediators able to modulate the inflammation process, vascular
87
thrombosis, muscle contraction, neurotransmission and pain (Ralevic and Burnstock, 1998;
Sitkovsky and Ohta, 2005; Sneddon et al., 1999; Burnstock, 2006; Desrosiers et al., 2007).
The adenosine also acts as a central nervous system (CNS) modulator in mammals, regulates
cell metabolism and triggers a variety of physiological effects participating in apoptosis,
necrosis and cell proliferation (Rathbone et al., 1999). NTPDase family (ecto-
diphosphohydrolase, apyrase or CD39) are responsible by hydrolyze ATP and ADP into
AMP, while 5'-nucleotidase hydrolyses AMP to adenosine (Zimmermann, 1996). The
adenosine deaminase (ADA) is responsible for the irreversible deamination of adenosine to
inosine, closely regulating extracellular adenosine concentrations (Franco et al., 1997).
In a previous study by our research group it was found an increased activity of
NTPDase and 5'nuclotidase (Oliveira et al., 2011b) and a decreased ADA activity in the
cerebral cortex of rats infected with T. evansi (Da Silva et al., 2011b). Reduction in serum
ADA activity was also detected (Da Silva et al., 2011a). Considering the functions of
nucleotides and nucleosides for CNS and hematological cells, as well as the clinical
alterations observed in trypanosomosis, this study aimed to evaluate the adenine nucleotides
and nucleoside concentration in serum and cerebral cortex of rats infected with T. evansi, to
confirm the results of enzymatic activity presented in other articles of the research group.
2. Material and methods
2.1. Experimental animals
Thirty outbreed male rats (mean age of 90 days) weighing 284 ± 12 g were kept in
cages in an experimental room with controlled temperature (25ºC) and humidity (70%). The
food (commercial ration) and water were disposed ad libitum. Previous to the experiment,
animals were submitted to an adaptation period of 15 days. The procedure was approved by
88
the Animal Welfare Committee of Universidade Federal de Santa Maria (UFSM), number
52/2009.
2.2. Experimental design and trypanosome infection
Rats were divided into two groups as follows: group A was constituted by 18 Wistar
rats inoculated with T. evansi strain and group B formed by 12 animals used as negative
controls. A strain of T. evansi obtained from a naturally infected dog was used (Colpo et al.,
2005), kept in liquid nitrogen at the laboratory. At day zero the parasites were thawed and the
number of trypanosomes per mL was determined using a hemocytometer under microscope
(Wolkmer et al., 2007). The animals from group A were inoculated intraperitoneally with
cryopreserved blood (0.2 mL) containing 1x106 trypomastigotes per animal. The control
animals received 0.2 mL of sterile saline (0.9% NaCl) by the same route.
Both groups were divided into two subgroups each, organized according to the time of
infection and degree of parasitemia. Two subgroups defined as controls (B4 and B20),
composed by six non-inoculated animals each, and the infected subgroups (A4 and A20),
inoculated with T. evansi, and set by six animals each. The animals were weighed at days 0, 4
and 20 PI.
2.3. Estimation of parasitemia
The presence and degree of parasitemia were determined daily for each animal by
blood film examination. A drop of blood was collected from the tail, placed on a slide and a
thin blood smear was prepared manually (Da Silva et al., 2006). The blood films were
Romanovsky stained and then examined under a microscope, counting 10 fields at 1000x of
magnification.
2.4. Collection of samples
The animals were anesthetized in a chamber with isoflurane for collection of blood by
cardiac puncture (3mL) at days 4 (A4 and B4) and 20 (A20 and B20) post-infection. The
89
material collected was allocated in tubes without anticoagulant to obtain serum. Thereafter,
animals were euthanized following recommendations of the Ethics Committee. The brains
were carefully removed avoiding contamination with peripheral blood, and cerebral cortex
was dissected. A portion of the cerebral cortex was used for biochemical analysis and a
histopathological study.
2.5. Samples preparation
2.5.1. Serum
ATP and its breakdown products were extracted according to Furstenau et al. (2008).
The denaturation of sample proteins was performed using 0.6mol/L perchloric acid. All
samples were then centrifuged (14000×g for 10min) and the supernatants were neutralized
with 4.0 N KOH and clarified with a second centrifugation (14000×g for 15 min) (Furstenau
et al., 2008).
2.5.2. Cerebral cortex
ATP and its breakdown products were extracted according to Ryder (1985). Briefly,
differents amounts of cortex were weighted and homogenized with 0.6 M perchloric acid at
0°C for 1 min with an Ultra-turrax homogenizer (model T 18, IKA® Works Inc., Wilmington,
Del., U.S.A.). The homogenate was centrifuged at 2000×g for 10 min, and the supernatant
was immediately neutralized to pH 6.5 to 6.8 with 1M potassium hydroxide.
2.6. Analysis of purines levels in serum and brain by high performance liquid
chromatography (HPLC)
High performance liquid chromatography (HPLC) was performed with a Shimadzu
(Kyoto, Japan) equipment composed of a model LC-20AT reciprocating pumps, a model
DGU-20A5 degasser, a diode array detector (DAD) model SPD-M20A, auto-sampler (SIL-
20A) and model CBM-20A integrator, operated by software LC Solution 1.22 SP1.
Separation was achieved with a Phenomenex Synergi 4µ Fusion RP-80A column (150 x 4.60
90
mm, 4 µm) with precolumn, using 0.04 M potassium dihydrogen orthophosphate (KH2PO4)
and 0.06 M dipotassium hydrogen orthophosphate (K2HPO4) as mobile phase A and
acetonitrile as mobile phase B. A gradient elution was used according to the specifications of
Scherer et al. (2005), at a flow rate of 0.7 mL/min. Mobile phases were filtered through a 0.45
µm Millipore filter prior to analysis, and all the reagent utilized were of HPLC grade. Purines
in the samples (ATP, ADP, AMP and adenosine) were identified by their retention times and
DAD spectrum (in the range 200-400 nm), and quantified by comparison of the peak's area
with standards. The results ATP, ADP, AMP and adenosine in serum were expressed by nmol
per L; and in brain were expressed by nmol per g of tissue.
2.7. Histopathology
Histopathologically, it was investigated a possible damage to the central nervous
system of rats infected with T. evansi. From sagittal sections with an interval of 3 mm in
region was a mounted slide of cerebral cortex. Slides were stained with hematoxylin and
eosin.
2.8. Statistical analysis
The data were presented as means and standard deviations analyzed by student t-test
(P < 0.05).
3. Results
3.1. Parasitemia and clinical course of infection
T. evansi could be detected in the blood of all infected rats from 24 to 48 h after
inoculation. Parasitemia levels increased progressively in most animals until day 4 PI, when
the first peak of parasitemia was observed (mean of 47 trypanosomes/field). In this first peak
of parasitemia, six infected rats maintained a progressive quantitative increase in blood
parasites and died between days 5–6 PI with high parasitemia (more than 200
91
trypanosomes/field). After day 5 PI, the remaining rats from subgroups A20 showed a
reduction in parasitemia, which oscillated from 0 to 2 parasites/field until day 20 PI. The
six rats which died were not used for nucleotides and nucleosides quantification.
At the time of sample collection, parasitemia of rats showed an average of 59 ± 9.7
trypanosomes/filed at day 4 PI (A4) and 1.6 ± 0.7 trypanosomes/field at day 20 PI (A20).
Animals from subgroup A4 showed weight loss (mean 287.6g to 274.9g), disorientation and
prostration. Rats from subgroup A20 also showed weight loss (282.1g to 277.3g). The
animals from control group remained clinically healthy during the experimental period.
3.2. Purines levels in serum
At day 4 PI it was observed a significant (P<0.05) increase in ATP (40%), AMP
(113%) and adenosine (54%) concentrations in serum of infected rats when compared to not-
infected. Similarly, at day 20 PI it was also observed an increased ATP (80%), AMP (61%)
and adenosine (481%) concentrations in serum of infected rats when compared to not-infected
(Figure 1). Concentration of ADP in serum of rats was not altered between groups (P>0.05;
Figure 1b).
3.3. Purines levels in cerebral cortex
At day 4 PI it was observed a significant (P<0.05) increase in both ATP (48%) and
AMP (44%) concentrations, while adenosine level was decreased (29%) in cerebral cortex of
infected rats when compared to not-infected (Figure 2). At day 20 PI it was observed an
increase in AMP (33%) and adenosine (36%) concentrations in cerebral cortex of infected rats
when compared to not-infected (Figure 2). Regarding the ATP levels, no difference was
observed between groups in day 20 PI (P>0.05). Concentrations of ADP in cerebral cortex
had no variation between groups (P>0.05; Figure 2b).
3.4. Histology
92
In subgroups A4 and A20 were not observed histological changes that give evidence
to damage in the cerebral cortex, as well as in group B.
4. Discussion
Increased NTPDase activity for the substrates ATP and ADP was observed in the brain
and reduced in platelets of infected rats with T. evansi at day 5 PI (Oliveira et al., 2011a;
2011b). In this study, we found an increased ATP concentration in serum and cerebral cortex,
unlike the levels of ADP which did not change between groups. The increase in ATP level
may be related to the inflammatory response and neurotoxicity, once it is an important
neutransmitter (Edwards et al., 1992; Agresti et al., 2005). According with Oliveira et al.
(2011b) the increased enzymatic activity may be associated with the elevated release of ATP,
which promotes an increase in the levels of intracellular calcium mediated by P2X receptors,
and this event could represent a significant damage to the cells (Edwards et al. 1992). Then
the increase in ATP level may cause the neurological alterations observed in infected rats
(Wolkmer et al., 2009; Oliveira et al., 2011b), because ATP could lead to excitotoxicity by
excitatory neurotransmitters release, such as glutamate (Lima et al., 2007). At day 15 PI,
Oliveira et al., (2011b) observed that a decrease in NTPDase activity may have a
compensatory effect in order to increase the concentrations of neurotransmitter (ATP) in the
brain of rats infected with T. evansi, but this was not confirmed in this study with 20 days PI,
because ATP level was not changed in the brain, unlike the serum concentration of the
nucleotide which was significantly increased.
In this study, no change was observed in ADP levels in serum and cerebral cortex,
although there were changes in enzymatic activity in rats infected with T. evansi, as well as by
increasing the NTPDase activity in the brain in day 5 PI and platelets in day 15 PI (Oliveira et
al., 2011a; 2011b). At 5 days PI there was a decrease in NTPDase activity in platelets
93
(Oliveira et al., 2011a). The ADP nucleotide, which is primarily released by platelets (Lee et
al., 1998), is mainly related to thrombocytopenia and platelet aggregation (Lunkes et al.
2004). However, in T. evansi infection occurred a severe decrease in platelets count (Oliveira
et al., 2011a), which could lead to reduction in ADP concentration. However, this was not
verified in this study, since the concentration of ADP was normal, probably due to an
increased release of this nucleotide by platelets, as a compensatory effect of coagulation
disorders.
The AMP concentration in both serum and brain increased significantly in rats infected
with T. evansi at days 4 and 20 PI, because the activation in the enzymatic cascade for
hydrolysis of ATP and ADP to AMP was identified by increased ectonucleotidases activity
(Oliveira et al., 2011a; 2011b). A previous study of our research group presented this
hypothesis, since there was an increased 5'-nucleotidase activity and consequently increased
AMP hydrolysis to adenosine, as observed in this study. At day 4 PI, despite the increased
activity of 5'-nucleotidase in the brain as previously described by Oliveira et al. (2011b) and
high concentration of AMP observed in this study, it was observed a decreased adenosine
level in cerebral cortex, probably due the increased requirement of this nucleoside during
infection, once adenosine is an important neuromodulador. Another hypothesis for the
reduction of adenosine at day 4 PI would be high parasitemia and severe deamination of
adenosine to inosine by ADA present in T. evansi according to Da Silva et al. (2011d).
In recent studies it was observed a reduction in ADA activity in serum, erythrocytes,
lymphocytes and cerebral cortex of rats infected with T. evansi compared to healthy rats after
4 days PI (Da Silva et al., 2011a; 2011b). According to the study aforementioned, the
reduction in ADA activity would have caused an increase in the extracellular concentrations
of adenosine, which would be converted to inosine. In this study it was confirmed
that indeed there was an increase in the concentration of adenosine in serum as suggested
94
by Da Silva et al. (2011a), but in cerebral cortex there was a reduction in adenosine levels.
According with literature, the increase of adenosine acts as a sensor and provides information
to the immune system about tissue injuries or acute inflammatory changes occurring in the
vicinity of the immune system (Kumar and Sharma, 2009). The interaction of adenosine with
adenosine receptors may promote anti-inflammatory effects, because it causes the inhibition
of Th1 immune response attenuating inflammation and tissue damage (Xaus et al., 1999).
Adenosine plays an important regulatory role in neuronal activity and has
neuroprotective actions in P1 purinoreceptor-mediated pathological conditions (Cunha and
Ribeiro, 2000; Cunha, 2001). Therefore, the reduction in cerebral cortex adenosine levels
after 4 days PI could be the cause of neurological disorders observed in rats infected with T.
evansi (Wolkmer et al., 2009; Tochetto et al., 2010; Da Silva et al., 2011b), once histological
lesions in brain are not observed in infected rats (Oliveira et al., 2011b), reconfirmed in this
study. At day 20 PI, the concentration of adenosine increased in serum and brain, probably in
the inflammatory response against the parasite and compensatory effects, because as
mentioned previously adenosine may inhibit the immune response and reduce cell and tissue
damage caused by inflammation.
The results allow us to conclude that infection with T. evansi in rats causes an increase
in the concentrations of ATP, AMP and adenosine in serum and cerebral cortex. This increase
in nucleotides and nucleosides levels associated with increased activities of ectonuclotidases
and ADA cause the activation of enzyme cascade with hydrolysis of ATP and ADP to AMP;
and AMP to adenosine. This nucleoside acts as an anti-inflammatory and neuromodulator
signaling molecule, in addition to other actions already mentioned in this manuscript. The
data show that increasing the activity of NTPDase and 5'nucleotidase consequently increase
the concentrations of ATP and AMP, and the reduction of ADA activity was designed to
increase the concentration of adenosine in accordance with literature.
95
References
Agresti, C., Meomartini, M.E., Amadio, S., Ambrosini, E., Serafini, B., Franchini, L., 2005.
ATP regulates oligodendrocyte progenitor migration, proliferation, and differentiation:
involvement of metabotropic P2 receptors. Brain Research 48, 157-165.
Berlin, D., Loeb, E., Baneth, G., 2009. Disseminated central nervous system disease caused
by Trypanosoma evansi in a horse. Veterinary Parasitology 161, 316–319.
Burnstock, G., 2006. Purinergic signaling – an overview. Novartis Found Symposium 276,
26–48.
Colpo, C. B., Monteiro, S. G. and Stainki, D. R., 2005. Natural infection by Trypanosoma
evansi in dogs. Ciencia Rural 35, 717-719.
Cunha, R.A., Ribeiro, J.A., 2000. ATP as presynaptic modulator. Life Science 68, 119–137.
Cunha, R.A., 2001. Adenosine as a neuromodulator and as homeostatic regulator in the
nervous system: different role, different sources and different receptors.
Neurochemistry International 38, 107–125.
Da Silva, A.S., Doyle, R.L., Monteiro, S.G., 2006. Método de contenção e confecção de
esfregaço sanguíneo para pesquisa de hemoparasitas em ratos e camundongos.
Faculdade de Zootecnia, Veterinária e Agronomia 13, 83–87.
Da Silva, A.S., Belle, L.P., Bitencourt, P.E.R., Costa, M.M., Oliveira, C.B., Moretto, M.B.,
Mazzanti, C.M., Lopes, S.T.A., Monteiro, S.G., 2011a. Activity of the enzyme
adenosine deaminase in serum, erythrocytes and lymphocytes of rats infected with
Trypanosoma evansi. Parasitology 138, 201-208.
Da Silva, A.S., Belle, L.P., Bitencourt, P.E.R., Perez, H.G., Thomé, G.R., Costa, M.M.,
Oliveira, C.B., Teixeira, M.M.G., Moretto, M.B., Mazzanti, C.M., Lopes, S.T.A.,
Monteiro, S.G., 2011b. Trypanosoma evansi: Adenosine deaminase activity in the brain
of infected rats. Experimental Parasitology 108, 173-177.
96
Da Silva, A.S., Monteiro, S.G., Gonçalves, J.F., Spanevello, R., Oliveira, C.B., Costa, M.M.,
Jaques, J.A.S, Morsch, V.M., Schetinger, M.R.C., Mazzanti, C.M., Lopes, S.T.A.,
2011c. Acetylcholinesterase activity and lipid peroxidation in the brain and spinal cord
of rats infected with Trypanosoma evansi. Veterinary Parasitology 175, 237-244.
Da Silva, A.S., Pimentel, V.C., Wolkmer, P., Oliveira, C.B., Miletti, L.C., Mazzanti, C.M.,
Lopes, S.T.A., Monteiro, S.G., 2011d. Biochemical detection of adenosine deaminase
in Trypanosoma evansi. Experimental Parasitology 128, 298–300.
Dávila, A.M.R., Silva, R.A.M.S., 2000. Animal trypanosomiasis in South America. Current
status, partnership, and information technology. Annals New York Academy Science
916, 199-212.
Desrosiers, M.D., Katherine, M.C., Fakir, M.J., Stephens, L.A., Jama, F.M., Shameli, A.,
Mehal, W.Z., Santamaria, P., Shi, Y., 2007. Adenosine deamination sustains dendritic
cell activation in inflammation. Journal of Immunology 179, 1884–1892.
Edwards, F.A., Gibb, A.J., Colquhoun, D., 1992. ATP receptor-mediated synaptic currents in
the central nervous system. Nature 359, 144–147.
Franco, R., Casado, V., Ciruela, F., Saura, C., Mallo, J., Canela, E. I., Llouis, C. (1997). Cell
surface adenosine deaminase: much more than an ectoenzyme. Progress Neurobiology
52, 283-294.
Furstenau, C.R., Trentin, D.S., Gossenheimer, A.N., Ramos, D.B., Casali, E.A., Chaves,
M.L.M.B., Sarkis, J.J.F., 2008. Ectonucleotidases activities are altered in serum and
platelets of L-NAME-treated rats. Blood Cells Molecular Disease 41, 223-229.
Gödeche, A. 2008. cAMP: fuel for extracellular adenosine formation? British Journal
Pharmacology 153, 1087–1089.
Gutierrez, C., Desquesnes, M., Touratier, L., Buscher, P., 2010. Trypanosoma evansi: recent
outbreaks in Europe. Veterinary Parasitology 174, 26-29.
97
Herrera, H.M., Davila, A.M., Norek, A., Abreu, U.G., Souza, S.S., Andrea, O.S., Jansen,
A.M., 2004. Enzootiology of Trypanosoma evansi in Pantanal, Brazil. Veterinary
Parasitology 125, 263-275.
Hoare, C. A., 1972. The Trypanosomes of mammals: a zoological monograph. Oxford,
Blackwell, 749pp.
Joshi, P. P., Shegokar, V. R., Power, R. M, Herder, S., Katti, R., Salkar, H. R., Dani, V. S.,
Bhargava, A., 2005. Human Trypanosomosis caused by Trypanosoma evansi in India:
the first case report. American Journal Tropical Medicine and Hygiene 73, 491–495.
Kumar, V., Sharma, A., 2009. Adenosine: an endogenous modulator of innate immune
system with therapeutic potential. European Journal Pharmacology 616, 7–15.
Lemos, K.R., Marques, L.C., Aquino, L.P., Alessi, A.C., Zacarias, R.Z., 2008. Astrocytic and
microglial response and histopathological changes in the brain of horses with
experimental chronic Trypanosoma evansi infection. Revista do Instituto de Medicina
Tropical de São Paulo 50, 243–249.
Lee, R.G., Bithell, T.C., Foerster, J., Athens, J.W., Lukens, J.N., 1998. Hematologia Clínica.
Manole, São Paulo.
Lima, R.R., Costa, A.M.R., De Souza, R.D., Gosmes-Leal, W., 2007. Degeneração neuronal
secundaria e excitotoxicidade. Revista Paranaense de Medicina 21, 27-31.
Lun, Z.R. and Desser, S. S., 1995. Is the broad range of hosts and geographical distribuition
of Trypanosoma evansi attributable to the loss of maxicircle kinetoplast DNA?
Parasitology Today 11, 131–133.
Lunkes, G., Lunkes, D., Morsch, V., Mazzanti, C., Morsch, A., Miron, V., Schetinger,
M.R.C. (2004). NTPDase and 5’-nucleotidase in rats alloxan induced diabetes. Diabetes
Research Clinical Practice 65, 1–6.
98
Menezes, V. T., Queiroz, A. O., Gomes, M. A., Marques, M. A., Jansen, A. M., 2004.
Trypanosoma evansi in inbred and Swiss–Webster mice: distinct aspects of
pathogenesis. Parasitology Research 94, 193–200.
Oliveira, C.B., Da Silva. A.S., Souza, V.C.G., Schetinger, M.R., Lopes, S.T.A., Leal, D.B.R.,
Monteiro, S.G., 2011a. Activities of adenine nucleotide and nucleoside degradation
enzymes in platelets of rats infected by Trypanosoma evansi. Veterinary Parasitology
178, 9-14.
Oliveira, C.B., Spanevello, R., Da Silva, A.S., Souza, V.C.G., Pimentel, V.C., Thomé, G.R.,
Schetinger, M.R., Lopes, S.T.A., Leal, D.B.R., Monteiro, S.G., 2011b. Trypanosoma
evansi: Activities of adenine nucleotide degradation enzymes in cerebral cortex of
infected rats. Experimental Parasitology 128, 225-229.
Ralevic, V., Burnstock, G., 1998. Receptors for purines and pyrimidines. Pharmacology
Research 50, 413-492.
Rathbone, M.P., Middlemiss, P.J., Gysbers, J.W., Andrew, C., Herman, M.A.R., Reed, J.K.,
Ciccarelii, R., Di Iorio, P., Caciagli, F., 1999. Trophic effects of purines in neurons and
glial cells. Progress Neurobiology 59, 663–690.
Rodrigues, A., Fighera, R.A., Souza, T.M., Schild, A.L., Barros, C.S., 2009. Neuropathology
of naturally occurring Trypanosoma evansi infection in horses. Veterinary Pathology
46, 251–258.
Ryder, J.M., 1985. Determination of adenosine triphosphate and its breakdown products in
fish products by high-performance liquid chromatography. Journal Agriculture Food
Chemistry 33, 678–680.
Scherer, R., Augusti, P.R., Steffens, C., Bochi, V.C., Hecktheuer, L.H., Lazzari, R., Radünz-
Neto, J., Pomblum, S.C.G., Emanuelli, T., 2005. Effect of Slaughter Method on
99
Postmortem Changes of Grass Carp (Ctenopharyngodon idella) Stored in Ice. Journal
of Food Science 70, 348-353.
Silva, R.A.M.S., Seidl, A., Ramirez, L., Dávila, A.M.R., 2002. Trypanosoma evansi e
Trypanosoma vivax: biologia, diagnóstico e controle. Corumbá, Embrapa Pantanal.
Sitkovsky, M.V., Ohta, A., 2005. The ‘danger’ sensors that STOP the immune response: the
A2 adenosine receptors? Trends Immunology 26, 299–304.
Sneddon, P., Westfall, T.D., Todorov, L.D., Mihaylova-Todorova, S., Westfall, D.P.,
Kennedy, C., 1999. Modulation of purinergic neurotransmission. Progress Brain
Research 20, 11–20.
Tochetto, C., Da Silva, A.S., Pierezan, F., Zanette, R.A., Monteiro, S.G., 2010. Paralisia dos
membros pélvicos em ratos infectados cronicamente com Trypanosoma evansi: relato
de caso. Faculdade de Zootecnia, Veterinária e Agronomia 17, 159-169.
Wolkmer, P., Da Silva, A. S., Carnelutti, J. F., Costa, M. M., Traesel, C., Lopes, S. T. A. and
Monteiro, S. G., 2007. Resposta eritropoética de ratos em diferentes de graus de
parasitemia por Trypanosoma evansi. Ciência Rural 37, 1682-1687.
Xaus, J., Valledor, A. F., Card, M., Marques, L., Beleta, J., Palacois, J. M., Celada, A., 1999.
Adenosine inhibits macrophage colony-stimulating factor-dependent proliferation of
macrophages through the induction of p27 kip-1 expression. Journal Immunology 163,
4140-4149.
Wolkmer, P., Da Silva, A. S., Carnelutti, J. F., Paim, F. C., Traesel, C., Lopes, S. T. A. and
Monteiro, S. G., 2009. Lipid peroxidation associated with anemia in rats experimentally
infected with Trypanosoma evansi. Veterinary Parasitology 165, 41-46.
Zimmermann, H. (1996). Biochemistry, localization and functional roles of ectonucleotidases
in the nervous system. Progress Neurobiology 49, 589–618.
100
Fig. 1: Concentration of ATP (A), ADP (B), AMP (C) and adenosine (D) in serum of rats
infected with Trypanosoma evansi (Day 4 and 20 PI) compared to not-infected (n=6).
(*p<0.05; **p<0.01)
101
Fig. 2: Concentration of ATP (A), ADP (B), AMP (C) and adenosine (D) levels in cerebral
cortex of rats infected with Trypanosoma evansi (Day 4 and 20 PI) compared to not-infected
(n=6). (*p<0.05; **p<0.01).
4 DISCUSSÃO
Nos últimos anos nosso grupo de pesquisa tem descrito diferentes casos de infecção
natural por T. evansi em bovinos, equinos e cães (DA SILVA et al., 2007; 2008; ZANETTE
et al., 2008) e investigado, experimentalmente a patogenia da doença em gatos (DA SILVA et
al., 2010) e, em ratos, como relatado nesta tese (Artigos: A-II e A-III; manuscrito: M-I).
Ratos infectados com T. evansi desenvolvem anemia, trombocitopenia, sinais neurológicos e
paralisia de membros pélvicos (DA SILVA et al., 2010; TOCHETTO et al., 2010), similar ao
que ocorre em equinos (SILVA et al., 1995).
Na patogenia da anemia por T. evansi, discute-se ter causas multifatoriais. Wolkmer et
al. (2009) concluiu que a peroxidação lipídica, causava a fragilidade da membrana
eritrocitária, levando à lise das hemácias. Em um estudo recente, Paim et al. (2011a) observou
que a infecção pelo flagelado causa um aumento significativo das citocinas pró-inflamatórias
no soro, e esta resposta imunológica afetaria a produção de células vermelhas. Conforme os
autores, o aumento das citocinas poderia contribuir em 24% para a anemia observada na
tripanossomose em ratos. A redução de acetilcolinesterase no sangue também pode contribuir
para a anemia (WOLKMER et al., 2010), pois esta enzima desempenha funções importantes
na superfície do eritrócito.
Neste estudo, foi envestigado o envolvimento do sistema purinérgico na anemia, para
isso foi mensurado a atividade da ADA no eritrócito. A alteração na atividade da ADA pode
estar envolvida em caso de anemia hemolítica (VALENTINE et al., 1977). A redução na
atividade da ADA em eritrócitos foi relacionada à diminuição de hematócrito (Artigo II). Para
confirmar esta relação, seria necessário analisar a expressão da ectoenzima na superfície das
células vermelhas do sangue. As hemáceas são relativamente bem supridas de ADA, portanto
estas células quando danificadas liberam quantidades significativas de ADA (MURAOKA et
al., 1990). Com base nessas informações, a hipótese seria que a atividade da ADA aumenta no
soro e/ou plasma, como consequência da diminuição dos glóbulos vermelhos devido a um
processo hemolítico (JACKSON et al., 1996). No entanto, isso não foi observado no Artigo II,
já que a atividade da ADA estava reduzida no soro. Embora, a correlação positiva entre
hematócrito e atividade da ADA em eritrócitos nada é conclusivo, portanto, mais estudos são
necessários para confirmar o papel da ADA na anemia causada por T. evansi em ratos.
Distúrbios de coagulação são comumente observados na tripanossomose por T. evansi.
103
O envolvimento do sistema purinérgico na hemostasia já está bem documentado, pois são as
plaquetas as grandes responsáveis pela secreção de nucleotídeos que desempenham funções
relacionadas à neurotransmissão (ATP), ativação da agregação plaquetária (ADP) e inibição
da agregação (adenosina). Em um estudo específico em plaquetas, Oliveira et al. (2011a)
observou que a hidrólise de ATP, ADP e AMP e desaminação da adenosina foram alterados
nas células de ratos infectados com T. evansi. Segundo o autor, durante o período de infecção,
a diminuição da atividade enzimática pode estar relacionada à trombocitopenia. Alterações
nas atividades dessas enzimas podem implicar na fisiopatologia da tripanossomose.
A infecção por T. evansi estimula a resposta imunológica, levando ao aumento de
imunoglogulinas (GRESSLER et al., 2010), citocinas (PAIM et al., 2011a) e proteínas de fase
aguda (COSTA et al., 2010). No hemograma, observou-se um aumento no número de
leucócitos totais em decorrência da linfocitose. Em um estudo recente conduzido pelo nosso
grupo de pesquisa (DA SILVA et al, 2011a,b), constatou-se que durante a fase aguda da
doença ocorreu um aumento da atividade da enzima AChE nos linfócitos, o que levaria,
consequentemente a um aumento na hidrólise de ACh, que tem ação anti-inflamatória, por
inibir a produção de mediadores inflamatórios, reduzindo os danos celulares e teciduais
durante a infecção. Neste estudo, verificamos que a ADA nos linfócitos desempenha função
similar, pois ocorreu redução na atividade da ADA a fim de aumentar as concentrações
extracelulares de adenosina, nucleosídeo que tem ação anti-inflamatória como discutido
detalhadamente no Artigo II. Conforme a literatura, a redução da atividade de ADA em
linfócitos levaria a interação da adenosina com receptores purinérgicos que existem em
muitos tipos de células, levando a efeitos anti-inflamatórios, entre eles a inibição da resposta
imune Th1. Na infecção aguda causada por T. cruzi, há uma predominância de Th1 e resposta
celular com produção de interferon-γ (KUMAR; TARLETON, 2001), assim como na
infecção por T. evansi relatada recentemente (PAIM et al., 2011a). Portanto, a inibição dessa
resposta pela ação da adenosina extracelular em receptores purinérgicos poderia atenuar a
inflamação e os danos teciduais.
Os distúrbios neurológicos são relatados em cavalos, camelos, búfalos, bovinos,
veados e gatos infectados por T. evansi (TUNTASUVAN et al., 1997; 2000; RODRIGUES et
al., 2005; BERLIN et al., 2009; DA SILVA et al., 2010). As lesões cerebrais foram relatadas
em bovinos e equinos (TUNTASUVAN et al., 1997; RODRIGUES et al., 2005). Ratos
infectados com o parasito e apresentando sinais neurológicos na fase aguda da doença não
apresentaram lesão histológica no SNC (OLIVEIRA et al., 2011a). Ao contrário, na fase
crônica os ratos apresentaram paralisia de membros pélvicos. Histologicamente, estes animais
104
apresentaram infiltrado inflamatório no encéfalo e lesões nos músculos pélvicos como
miosite, degeneração valeriana, atrofia das fibras e infiltrados inflamatórios (DA SILVA et
al., in press). Com base nestas informações, pode-se sugerir que os sinais clínicos observados
na fase aguda são causados por alterações nas concentrações de neurotransmissores (ATP e
ACh) e neuromodulador (adenosina) em animais infectados com T. evansi, como apresentado
no Artigo III. Outro elemento importante na neurotransmissão é o óxido nítrico, que em ratos
infectados com T. evansi encontrou-se elevado em diferentes regiões do encéfalo (PAIM et
al., 2011b). Conforme, a literatura, o excesso de óxido nítrico no SNC pode levar a
citotoxidade, causando lesões histológicas em células nervosas, o que não foi verificado no
manuscrito I.
Como mencionado anteriormente, ratos são altamente suscetíveis à tripanossomose,
apresentando alterações hematológicas, bioquímicas e patológicas associadas com ataxia,
tremores e coma terminal de animais não tratados (MENEZES et al., 2004; WOLKMER et
al., 2009). A infecção humana por T. evansi foi relatada pela primeira vez em 2005, em um
agricultor indiano que mostrou alterações comportamentais, tais como: desorientação, ataxia e
déficits sensoriais (JOSHI et al., 2005). Relacionando estas alterações com nosso estudo
(Artigo III), verificamos que a redução da atividade da ADA em algumas regiões do cérebro
(córtex cerebral, estriado e hipocampo) poderia ter aumentado os níveis de adenosina, porém
isso não ocorreu. Nos ratos com sinais neurológicos, na fase aguda, observamos redução na
concentração de adenosina (Manuscrito I). Então, como a adenosina desempenha um
importante papel de regulador da atividade neuronal e tem ações neuroprotetoras em P1
purinoreceptor mediada por condições patológicas (CUNHA; RIBEIRO, 2000; CUNHA,
2001), sua deficiência poderia causar os distúrbios neurológicos já observados e relatados em
infecções por este parasito.
A enzima ADA é amplamente distribuída em tecidos e fluídos de mamíferos em duas
isoformas, ADA1 e ADA2. Em células teciduais, principalmente sistema nervoso predomina
a isoforma ADA1 e a isoforma de ADA2 é encontrado no soro e na superfície de células
sanguíneas. Uma expressão heterogênea da atividade da ADA pode ser encontrada entre as
células periféricas e, até mesmo, dentro das distintas regiões do SNC em uma mesma
condição patológica (FRANCO et al, 1986, 1997). Nestes estudos (Artigos II e III), foi
observada heterogenidade na atividade da ADA no soro, linfócitos, eritrócitos, plaquetas que
predomina ADA2 e regiões do encéfalo que predomina ADA1. Estas diferenças na atividade
enzimática podem ser explicadas pelas duas isoformas da ADA, e também, pela diferentes
funções que a ADA desempenha nas células e tecidos.
105
No Artigo I tivemos como objetivo de investigar a presença de ADA em T. evansi,
uma enzima importante para muitas funções vitais nos mamíferos e, possivelmente para o
parasito também. Esta enzima já havia sido detectada no genoma de T. brucei, assim como foi
detectado no T. evansi por técnicas bioquímicas. A ideia de investigar a presença desta
enzima no parasito surgiu no momento que foi detectado o T. evansi no encéfalo dos ratos
infectados, pela técnica de PCR (Artigo III). Como as análises bioquímicas são realizadas a
partir de homogenizado da estrutura cerebral, possivelmente a ADA do parasito poderia ser
detectada no teste bioquímico juntamente com a ADA do hospedeiro. No entanto, na maioria
das estruturas dos animais infectados foi verificado redução da atividade da ADA.
Em um dos nossos estudos foi verificado um aumento da atividade da NTPDase e 5'-
nucleotidase (OLIVEIRA et al., 2011a) e uma redução na atividade da ADA no córtex
cerebral de ratos infectados com T. evansi (Artigo III); e redução e/ou aumento da atividade
da ADA no soro, eritrócitos e linfócitos (Artigo II). Considerando que estas enzimas são
responsáveis pela regulação da concencentração de nucleotídeos e nucleosídeos de adenina no
SNC e em células hematológicas, outro estudo conduzido pelo nosso grupo de pesquisa teve a
finalidade de mensurar os níveis de ATP, ADP, AMP e adenosina no soro e encéfalo de ratos
infectados com o parasito (Manuscrito I).
Conforme mencionado anteriormente, a atividade da enzima NTPDase aumentou para
os substratos ATP e ADP no cérebro (OLIVEIRA et al., 2011a) e reduziu em plaquetas
(OLIVEIRA et al., 2011b) de ratos infectados com T. evansi no dia 5 PI. No manuscrito I, foi
observado um aumento na concentração de ATP no córtex cerebral e no soro, ao contrário dos
níveis de ADP que não alterou entre os grupos. O aumento do ATP pode estar relacionado
com a resposta inflamatória e neurotoxicidade, devido ao fato de ser um importante
neutransmissor (EDWARDS et al., 1992; AGRESTI et al., 2005). O aumento da atividade
enzimática pode estar associado à elevada liberação de ATP, que promove um aumento nos
níveis de cálcio intracelular mediada por receptores P2X, e esse evento poderia representar
um prejuízo significativo para as células (EDWARDS et al., 1992). Então, o aumento no nível
de ATP pode causar as alterações neurológicas observadas em ratos infectados (WOLKMER
et al., 2009; OLIVEIRA et al., 2011a), porque o ATP pode levar a excitotoxicidade por
liberação de neurotransmissores excitatórios, como o glutamato (LIMA et al., 2007). No dia
15 PI, pesquisadores observaram uma diminuição na atividade da NTPDase explicada como
um efeito compensatório (OLIVEIRA et al., 2011a), a fim de aumentar a concentração do
neurotransmissor (ATP) no cérebro de ratos infectados com T. evansi. Esse fato não foi
confirmado com 20 dias PI (Manuscrito I), porque os níveis de ATP não diferiram no cérebro,
106
ao contrário da concentração sérica do nucleotídeo que foi significativamente elevada.
Nenhuma mudança foi observada nos níveis de ADP no córtex cerebral e soro
(Manuscrito I), embora haja alteração na atividade enzimática dos ratos infectados com T.
evansi, como o aumento da atividade da NTPDase no encéfalo (OLIVEIRA et al., 2011a) e
plaquetas (OLIVEIRA et al., 2011b) no dia 5 e 15 PI, respectivamente. Já no dia 5 PI, houve
uma diminuição na atividade da NTPDase em plaquetas (OLIVEIRA et al., 2011b). O ADP
está relacionada principalmente à trombocitopenia e agregação plaquetária (LUNKER et al.,
2004), sendo que o ADP é secretado principalmente pelas plaquetas (LEE et al., 1998). No
entanto, na infecção por T. evansi ocorreu severa redução de plaquetas (OLIVEIRA et al.,
2011b), o que poderia levar à redução na concentração de ADP. Porém verificou-se que a
concentração de ADP foi similar ao grupo controle, provavelmente devido a um aumento da
secreção destes nucleotídeos por plaquetas, como resposta aos distúrbios de coagulação.
A concentração de AMP no soro e no cérebro aumentou significativamente em ratos
infectados com T. evansi no dia 4 e 20 PI (Manuscrito I), isso poderia ser explicado pela
ativação da cascata enzimática na hidrólise de ATP e ADP para AMP, já que houve um
aumento na atividade das ectonucleotidases (OLIVEIRA et al., 2011a,b). Na sequência da
cascata, o aumento na atividade da enzima 5'-nucleotidase, gera consequentemente um
aumentou na hidrólise de AMP para adenosina, como observado no Manuscrito I. No dia 4 PI,
apesar do aumento da atividade da enzima 5'-nucleotidase no córtex cerebral previamente
descrito por Oliveira et al. (2010a) e alta concentração de AMP descrita no Manuscrito I,
observamos que a redução dos níveis de adenosina no córtex cerebral, provavelmente ocorreu
devido a uma maior exigência deste nucleosídeo durante a infecção, já que a adenosina é um
neuromodulador importante. Outra hipótese para a redução da adenosina no dia 4 PI, seria a
elevada parasitemia, a qual proporcionaria uma maior degradação de adenosina em inosina
pela ADA presentes no T. evansi, uma enzima que foi detectada neste estudo (Artigo I).
No Manucrito II foi relatada uma redução na atividade da ADA no soro, eritrócitos,
linfócitos e córtex cerebral de ratos infectados com T. evansi em comparação com ratos
saudáveis no dia 4 PI. Segundo o estudo, a redução da atividade da ADA ocorreu devido ao
aumento na concentração extracelular de adenosina, a qual seria convertido em inosina. No
Manuscrito I foi confirmado que realmente houve um aumento na concentração de adenosina
no soro como sugerido no Artigo II. Já no córtex cerebral, houve uma redução nos níveis de
adenosina (Manuncrito I). Conforme a literatura, o aumento de adenosina pode ser um sensor,
fornecendo informações para o sistema imunológico sobre o dano tecidual ou alterações
inflamatórias agudas (KUMAR; SHARMA, 2009). A interação da adenosina a receptores de
107
adenosina pode ter um efeito anti-inflamatório, levando à inibição da resposta imune mediada
por Th1, e reduzindo o processo inflamatório e os danos teciduais (XAUS et al., 1999).
Como já mencionado, a adenosina desempenha um importante papel regulador na
atividade neuronal. Portanto, a redução dos níveis de adenosina no córtex cerebral no dia 4 PI
(Manuscrito I) poderia ser a causa dos distúrbios neurológicos observados em ratos infectados
com T. evansi (WOLKMER et al., 2009; TOCHETTO et al., 2010; OLIVEIRA et al., 2011a),
já que lesões histológicas no cérebro não são observados em ratos infectados (OLIVEIRA et
al., 2011a). No dia 20 PI, a concentração de adenosina no cérebro e soro aumentou,
provavelmente devido à adenosina ser capaz de inibir a resposta imune, e assim reduzir dano
celular e tecidual devido ao processo inflamatório.
5 CONCLUSÃO
Neste estudo concluiu-se que o Trypanosoma evansi apresenta em sua composição
química a enzima ADA, que deve ser responsável pela desaminação de adenosina em inosina
no parasito, similar ao que ocorre nos mamíferos;
O estudo com ratos infectados, experimentalmente, com T. evansi permitiu elaborar
algumas conclusões relacionas ao sistema purinérgico, descritas a seguir: (1) a redução na
atividade ADA nos eritrócitos pode estar relacionada à patogenia da anemia nas
tripanossomoses; (2) a redução da atividade da ADA no soro, eritrócitos e linfócitos ocorreu
com a finalidade de aumentar as concentrações de adenosina extracelular, que tem caráter
anti-inflamatório a fim de minimizar o processo inflamatório e danos teciduais causado pela
infecção.
Na análise dos nucleotídeos e nucleosídeo também possibilitou fazer conclusões
como: (1) o aumento de ATP e redução de adenosina no córtex cerebral pode ser responsável
pelos sinais neurológicos observados na fase aguda da doença; (2) a redução da atividade da
ADA no encéfalo ocorreu para aumentar as concentrações de adenosina, fundamental para a
neuromudulação durante o parasitismo.
REFERÊNCIAS
AGRESTI, C. et al. ATP regulates oligodendrocyte progenitor migration, proliferation, and differentiation: involvement of metabotropic P2 receptors. Brain Research, Philadalphia, v.48, p.157-165, abr. 2005. ALDRICH, M. et al. The importance of adenosine deaminase for lymphocyte development and function. Biochemical and Biophysical Research Communications, New York, v.272, p.311-335, jun. 2000. ALTUG, N. et al. Determination of adenosine deaminase activity in cattle naturally infected with Theileria annulata. Tropical Animal Health Production , Midlothian, v.40, p.449-456, agost. 2008. AMER, S., et al. Molecular identification and phylogenetic analysis of Trypanosoma evansi from dromedary camels (Camelus dromedarius) in Egypt, a pilot study. Acta Tropica, Japão, v.117, p.39-46, jan. 2011. ANFOSSI, G, et al. Adenosine increases human platelet levels of cGMP through nitric oxide: possible role in its antiaggregating effect. Thrombosis Research, San Diego, v.105, p.71-78, jan. 2002. ANOSA, V. O.; KANEKO, J. J. Pathogenesis of Trypanosoma brucei infection in deer mice (Peromyscus maniculatus): light and electron microscopic studies on erythrocyte pathologic changes and phagocytosis. American Journal of Veterinary Research, New York, v. 44, n. 4, p. 645-651, abr. 1983. ARAN, J. M. et al. Presence of adenosine deaminase on the surface of mononuclear cells: immunochemical localization using light and electron microscopy. Journal of Histochemistry & Cytochemistry, EUA, v.39, p.1001-1008, agost. 1991. ATARHOUCH, T. et al. Camel trypanosomosis in Marocco 1: results of a first epidemiological survey. Veterinary Parasitology, Amsterdam, v. 111, n. 4, p. 277-286, abr. 2003. ATKINSON, B. et al. Ecto-nucleotidases of CD39/NTPDase family and thrombus formation: potencial as therapeutic targets. Blood Cells Molecules and Diseases, New York, v.36, p.217-222, mar. 2006.
110
BARAL, T.N. et al. Control of Trypanosoma evansi infection is IgM mediated and does not require a type I inflammatory response. Journal of Infectious Disease, Chicago, v.195, p.1513–1520, dez. 2007. BERLIN, D. et al. Disseminated central nervous system disease caused by Trypanosoma evansi in a horse. Veterinary Parasitology, Amesterdam, v.161, p.316–319, abr. 2009. BOURS, M.J.L. et al. Adenosine 5′- triphosphate and adenosine as endogenous signaling molecules in immunity and inflammation. Pharmacology and Therapy, New York, v.112, p.358- 404, nov. 2006. BRANDÃO, J. P. et al. Natural infection by Trypanosoma evansi em dog – Case report. Clínica Veterinária, São Paulo, n. 36, p. 23-26, jan. 2002. BRUN, R. et al. Trypansosoma evansi and T. equiperdum: distribution, biology, treatment and phylogenetic relationship (a review). Veterinary Parasitology, Amsterdam, v. 79, n. 1, p. 95-107, jan. 1998. BURNSTOCK, G. Purinergic signalling and vascular cell proliferation and death. Arteriosclerosis Thrombosis Vascular Biology, New York, v.22, p.364–373, mai. 2002. BURNSTOCK, G.; KNIGHT, G. E. Cellular distribution and functions of P2 receptor subtypes in different systems. International Review of Cytology, Knoxville, v. 240, p.31–304, jan. 2004. BURNSTOCK, G. Purinergic signaling – an overview. Novartis Found Symposium, Chicago, v.276, p.26–48, jan. 2006. CARRINGTON, M. et al. Variant specific glycoprotein of Trypanosoma brucei consists of two domains each having an independently conserved pattern of cysteine residues. Journal of Molecular Biology, La Jolla, v.221, p.823–835, out. 1991. CIRUELA, F. et al. Adenosine deamianse affects ligand-induced signalling by interacting with cell surface adenosine receptors. FEBS letters, Heidelberg, v.380, p.219-223, mai. 1996. CODERO, O. et al. Cytokines regulate membrane adenosine deaminase on human activated lymphocytes. Journal of Leukocyte Biology, Barcelona, v.70, p.920–930, nov. 2001.
111
COLPO, C. B. et al. Infecção natural por Trypanosoma evansi em cães. Ciência Rural, Santa Maria, v. 35, n. 3, p. 717-719, maio/jun. 2005. CONRADO, A. C. et al. Infecção natural por Trypanosoma evansi em cavalos na região central do estado do Rio Grande do Sul. Ciência Rural, Santa Maria, v. 35, n. 4, p. 928-931, jul./ago. 2005. CONNOR, R. J.; VAN DEN BOOSCHE, P. African animal trypanosomoses. In: COETZER, J. A. W.; TUSTIN, R. C. (Eds.). Infectious diseases of livestock. 2nd ed. South Africa: Oxford University Press, 2004. v.1. cap.12, p.251-296. COSTA, M.M. et al. Serum proteinogram of cats experimentally infected by Trypanosoma evansi. Preventive Veterinary Medicine, Colorado, v.95, p.301–304, abr. 2010. CRISTALLI, G.E et al. Adenosine deaminase: functional implications and different classes of inhibition. Medicinal Research Reviews, Malden, v.21, p. 105–128, fev. 2001. CUNHA, R.A.; RIBEIRO, J.A. ATP as presynaptic modulator. Life Science, Tuscon, v.68, p.119–137, fev. 2000. CUNHA, R.A. Adenosine as a neuromodulator and as homeostatic regulator in the nervous system: different role, different sources and different receptors. Neurochemistry International , Budapest, v.38, p.107–125, jan. 2001. DA SILVA, A.S. et al. Ocorrência de Trypanosoma evansi em bovinos de uma propriedade leiteira no município de Videira SC. Acta Scientiae Veterinariae, Porto Alegre, v.35, n.3, p.373-376, 2007. DA SILVA, A.S. et al. Sinais Clínicos em cães naturalmente infectados por Trypanosoma evansi (Kinetoplastida: Trypanosomatidae) no Rio Grande do Sul, Brasil. Clínica Veterinária, São Paulo, v.8, n.72, p. 66-68, 2008. DA SILVA, A. S. et al. Diminazene aceturate in the control of Trypanosoma evansi infection in cats. Veterinary Parasitology, Amsterdam, v. 165, p, 47-50, 2009. DA SILVA, A.S. et al. Clinical aspects of cats experimentally infected with Trypanosoma evansi. Comparative Clinical Pathology, Alemanha, v.19, p.85-89, jan. 2010.
112
DA SILVA, A.S. et al. Acetylcholinesterase activity and lipid peroxidation in the brain and spinal cord of rats infected with Trypanosoma evansi. Veterinary Parasitology, Amsterdam, v.175, p.237-244, 2011a. DA SILVA, A.S. et al. Susceptibility of Trypanosoma evansi to cordycepin. Biomedicine & Pharmacotherapy, Alemanha, v.65, p.220–223, 2011b. DA SILVA, A.S. et al. Clinical signs and histopathology of brain, spinal cord and muscle of the pelvic limb of rats experimentally infected with Trypanosoma evansi. Pathology - Research and Practice. In press. DESROSIERS, M.D. et al. Adenosine deamination sustains dendritic cell activation in inflammation. Journal of Immunology, Bethesda, v.179, p.1884–1892, dez. 2007. DOCAMPO, R.; MORENO, S.N. The role of Ca2+ in the process of cell invasion by intracellular parasites. Parasitology Today, EUA, v.12, p.61–65, jan. 1996. EDWARDS, F. A. et al. ATP receptor-mediated synaptic currents in the central nervous system. Nature, New York, v.359, p.144–147, jan. 1992. FRANCISCATO, C. et al. Dog naturally infected by Trypanosoma evansi in Santa Maria, RS, Brasil. Ciência Rural, Santa Maria, v.37, n.1, p. 288-291, jan. 2007. FRANCO, R. et al. Heterogeneous localization of some purine enzymes in subcellular fractions of rat brain and cerebellum. Neurochemical Research, New York, v.11, p.423–435, 1986. FRANCO, R. et al. Cell surface adenosine deaminase: much more than an ectoenzyme. Progress in Neurobiology, Pittsburgh, v.52, p.283-294, mar. 1997. FRANKE, C. R. et al. Investigation on naturally ocurring T. evansi infections in horses, cattle, dogs and capybaras (Hydrochaeris hydrochaeris) in Pantanal de Poconé (Mato Grosso, Brazil). Acta Tropica, Japão, v. 58, n. 2, p. 159-69, fev. 1994. GESSI S. et al. Adenosine receptors in colon carcinoma tissues and colon tumoral cell lines: Focus on the A3 adenosine subtype. Journal of Cellular Physiology, West Sussex, v.211, n.3. p.826–836, nov. 2007.
113
GREIGER, J.D., NAGY, J.I. Distribution of adenosine deaminase activity in rat brain and spinal cord. Journal of Neuroscience, Santiago, v.6, p.2707-2714, dez. 1986. GRESSLER, L.T. et al. Niveis de imunoglobulinas em ratos infectados com Trypanosoma evansi. Ciencia Animal Brasileira, Goiânia, v.11, n.1, p.201-204, jan./mar. 2010. HASKO, G.; CRONSTEIN, B.N. Adenosine: an endogenous regulator of innate immunity. Trends Immunology, Cambridge, v.25, p.33-39, jan. 2004. HERRERA, H. M. et al. Enzootiology of Trypanosoma evansi in Pantanal, Brazil. Veterinary Parasitology, Amsterdam, v. 125, n. 3-4, p. 263-275, nov. 2004. HOARE, C. A. The Trypanosomes of mammals: a zoological monograph. Oxford: Blackwell, 1972. 749p. IWAKI-EGAWA, S. et al. Adenosine deaminase 2 from chicken liver: purification, characterization, and N-terminal amino acid sequence. Comparative Biochemistry and Physiology. Part B, Biochemistry & Molecular Biology, Victoria, v.137, p.247-254, mar. 2004. JACKSON, E.K. et al. Injured erythrocytes release adenosine deaminase into the circulation. Journal of Pharmacology and Experimental Therapeuties, Chicago, v.279, 1250–1260, dez. 1996. JOSHI, P. P. et al. Human Trypanosomosis caused by Trypanosoma evansi in India: the first case report. American Journal of Tropical Medicine and Hygiene, New York, v. 73, n. 3, p. 491-495, mar. 2005. KHAMBU, B. et al. Serum nitrite level and adenosine deaminase activity is altered in visceral Leishmaniasis. Nepal Medical College Journal, San Diego, v.9, p.40–43, jan. 2007. KOBAYASHI, F.; IKEDA, T.; MARUMO, F.; SATO, C. Adenosine deaminase isoenzymes in liver disease. The American Journal of Gastroenterology, New York, v. 88, p. 226-271, mar. 1993. KUBIAK, G. V. L.; MOLFI, A. Tripanosomíase eqüina (Mal das Cadeiras). Curitiba: Instituto de Biologia e Pesquisas Tecnológicas do Estado do Paraná. Tip. João Haupt, 1954. 51p. (Boletim n.33).
114
KUMAR, S.; TARLETON, R.L. Antigen-Specific Th1 But Not Th2 Cells Provide Protection from Lethal Trypanosoma cruzi Infection in Mice. Journal of Immunology, EUA, v.166, p.4596-4603, dez. 2001. KUMAR, V.; SHARMA, A. Adenosine: an endogenous modulator of innate immune system with therapeutic potential. European Journal Pharmacology, Netherlands, v.616, p.7–15, jan. 2009. LEE, R.G. et al. Hematologia Clínica. Manole, São Paulo, 1998. LEVINE, N. D. Protozoan parasites of domestic animals and of man. 2nd ed. Minneapolis: Burgess Publishing Company, 1973, 406p. LIMA, R.R, et al. Degeneração neuronal secundaria e excitotoxicidade. Revista Paranaense Medica, Curitiba, v.21, p.27-31, jan. 2007. LUNKES, G. et al. NTPDase and 5’-nucleotidase in rats alloxan induced diabetes. Diabetes Research Clinical Practice, Autralia, v.65, p.1–6, jan. 2004. MAUDLIN, I. et al. The Trypanosomiases. Wallingford: CABI Publishing. 2004. 640p. MELO, F.A.F. et al. Diagnóstico da tuberculose pleural pela ADA, isolada ou combinada a outras variáveis, inclusive em HIV-positivos. Folha Médica, São Paulo, v.119, p.9-21, mar. 2000. MENEZES, V.T. et al. Trypanosoma evansi in inbred and Swiss–Webster mice: distinct aspects of pathogenesis. Parasitology Research, Alemnha, v.94, p.193–200, fev. 2004. MIJARES, A. et al. Immune detection of acetylcholinesterase in subcellular compartments of Trypanosoma evansi. Parasitology Research, Alemanha, v.108, p.1-5, jan. 2011. MURAOKA, T. et al. Automated enzymatic measurements of adenosine deaminase isozymes activities in serum. Analytical Biochemistry, Bethesda, v.187, v.278-282, fev. 1990. OLIVEIRA, C.B. et al. Activities of adenine nucleotide and nucleoside degradation enzymes in platelets of rats infected by Trypanosoma evansi. Veterinary Parasitology, Amesterdam, v.178, p.9-14, 2011a.
115
OLIVEIRA, C.B. et al. Trypanosoma evansi: Activities of adenine nucleotide degradation enzymes in cerebral cortex of infected rats. Experimental Parasitology, Hertfordshire, v.128, p.225-229, 2011b. OMER, O.H. et al. Study on the antioxidant status of rats experimentally infected with Trypanosoma evansi. Veterinary Parasitology, Amesterdam, v.145, 142–145, fev. 2007. OTTO, M.A. et al. Susceptibility of Trypanosoma evansi to human blood and plasma in infected mice. Veterinary Parasitology, Amesterdam, v.168, p.1-4, 2010. OZCAN, E. et al. Serum erythrocyte and leukocyte adenosine deaminase activities in patients with vivax malaria in Turkey. Journal of the Egyptian Society of Parasitology, Egito, v.27, p.445–454, mai. 1997. PAIM, F.C. et al. Cytokines in rats experimentally infected with Trypanosoma evansi. Experimental Parasitology, Hertfordshire, v.128, p.365-370, agost. 2011a. PAIM, F.C. et al. Trypanosoma evansi: Concentration of 3-nitrotyrosine in the brain of infected rats. Experimental Parasitology, Hertfordshire, PRELO, 2011b. PAYS, E. et al. Antigenic variation in Trypanosoma brucei: facts, challenges and mysteries. Current Opinion in Microbiology , EUA. v.7, p.369–374, jun. 2004. PEREGRINE, A.S.; MAMMAN, M. Pharmacology of Dimenazene: A Review. Acta Tropical , Japão, v. 54, n. 2, p. 185-203, fev. 1993. RAMIREZ, L. E. et al. La tripanosomiasis in los animals domesticos em Colombia. Colombia: Centro Internacional de Agricultura Tropical, 1979. RATHBONE, M.P. et al. Trophic effects of purines in neurons and glial cells. Progress in Neurobiology, Pittsburgh, v.59, p.663–690, jul. 1999. ROTTENBERG, M.E. et al. Treatment of African trypanosomiasis with cordycepin and adenosine deaminase inhibitors in a mouse model. Journal of Infection Disease, EUA, v.192, p.1658-1665, nov. 2005. RODRIGUES, A. et al. Outbreaks of trypanosomiasis in horses by Trypanosoma evansi in the state of Rio Grande do Sul, Brazil: epidemiological, clinical, hematological, and pathological aspects. Pesquisa Veterinária Brasileira, Rio de Janeiro, v.25, n. 4, p. 239-249, dez. 2005.
116
ROMANOWSKA, M. et al. Adenosine ecto-deaminase (ecto-ADA) from porcine cerebral cortex synaptic membrane. Brain Research, Philadalphia, v.1156, p.1-8, 2007. SABOURY, A.A. et al. Inhibition study of adenosine deaminase by caffeine using spectroscopy and isothermal titration calorimetry. Acta Biochimica Polonica, Polonia, v.50, p.849–855, out. 2003. SANCHEZ, M., et al. Six related nucleoside/nucleobase transporters from Trypanosoma brucei exhibit distinct biochemical functions. Journal Biology Chemistry, Rockville, v.277, p.21499-21504, dez. 2002. SAURA, C. et al. Adenosine deaminase interacts with A1 adenosine receptors in pig brain cortical membranes. Journal of Neurochemistry, Seattle, v.66, p.1675-1682, nov. 1996. SCHETINGER, M.R.C. et al. NTPDase and 5'-nucleotidase activities in physiological and disease conditions: new perspectives for human health. BioFactors (Oxford), Inglaterra, v. 31, p. 77-98, jan. 2007. SHEGOKAR, V. R. et al. Short report: human trypanosomiasis caused by Trypanosoma evansi in a village in India: preliminary serologic survey of the local population. American Journal of Tropical Medicine and Hygiene, New York, v.75, n.5, p.869–870, mai. 2006. SHEHU, S. A. et al. Neuraminidase (Sialidase) activity and its role in development of anaemia in Trypanosoma evansi infection. Journal of Applied Sciences, San Diego, v.6, n.13, p.2779-2783, dez. 2006. SILVA, R.A.M.S. et al. Trypanosomosis outbreaks due to Trypanosoma evansi in the Pantanal, Brazil: a preliminary approach on risk factors. Revue D’Élevage et de Médicine Véterinaire des Pays Tropicaux, France, v.4, n.3, p.315-319, set. 1995. SILVA, R.A.M.S. et al. Trypanosoma evansi e Trypanosoma vivax: biologia, diagnóstico e controle. Corumbá: Embrapa Pantanal. 2002. 141p. SITKOVSKY, M.V.; OHTA, A. The ‘danger’ sensors that STOP the immune response: the A2 adenosine receptors? Trends Immunology, Cambridge, v.26, p.299–304, mai. 2005. SOSLAU, G.; YOUNGPRAPAKORN, D. A possible a dual physiological of extracellular ATP modulation of platelet aggregation. Biochemistry Biophysica Acta, New York, v.1355, p.131-140, fev. 1997.
117
SUSWAM, E.A. et al. Changes in properties of adenosine transporters in Trypanosoma evansi and modes of selection of resistance to the melaminophenyl arsenical drug, Mel Cy. Veterinary Parasitology, Amesterdam, v.102, p.193–208, mar. 2001. SUSWAM, E.A. et al. Changes in adenosine transport associated with melaminophenyl arsenical (Mel CY) resistance in Trypanosoma evansi: down-regulation and affinity changes of the P2 transporter. Parasitology, London, v.127, p.543–549, 2003. TAVARES, K.C. Biossíntese de selenocisteína em Trypanosoma evansi. Dissertação. 91f. Dissertação apresentada ao Curso de Mestrado em Ciência Animal, do Centro de Ciências Agroveterinárias da Universidade do Estado de Santa Catarina, Lages, 2011. TOCHETTO, C. et al. Paralisia dos membros pélvicos em ratos infectados cronicamente com Trypanosoma evansi: relato de caso. Faculdade de Zootecnia, Veterinária e Agronomia, Uruguaiana, v.17, p.159-169, jan/jun. 2010. TONIN, A.A. et al. Trypanosoma evansi: Ca2+ ATPase activity and lipid peroxidation in skeletal muscle from rats experimentally infected. Experimental Parasitology, Hertfordshire, v.128, 177-181, agost. 2001. TOURANTIER, L. First international seminar on nom Tsétse transmitted animal rypanosomes: conclusions and recomendations. Review Science Technology Office International Epizootic, Europe, v.12, n.1, p.273-281, jan.1993. TUNTASUVAN, D. et al. Cerebral trypanosomiasis in native cattle. Veterinary Parasitology, Amsterdam, v.73, n.4, p.357-363, apr. 1997. TUNTASUVAN D.; LUCKINS A. G. Status of Surra in Thailand. The Journal of Tropical Medicine and Parasitology, Londres, v. 21, n. 1, p. 1-8, jan. 1998. TUNTASUVAN, D. et al. Detection of Trypanosoma evansi in brains of the naturally infected hog deer by immunohistochemistry. Veterinary Parasitology, Amsterdam, v.87, n. 3, p.223-230, mar. 2003. VALENTINE, W.N. et al. Hereditary hemolytic anemia with increased adenosine deaminase (45-70 fold) and decreased adenosine tniphosphate. Science, San Diego, v.195, 783, 1977. VANHAMME, L. et al. Apolipoprotein L-1 is the trypanosome lytic factor of human serum. Nature, New York, v.422, p.83–87, jan. 2003.
118
VANHOLLEBEKE, B. et al. Human Trypanosoma evansi infection linked to a lack of apolipoprotein L-I. New Englat Journal Medicine, London, v.355, p.2752–2756, nov. 2006. VENTURA, R. M. et al. Molecular and morphological studies of Brazilian Trypanosoma evansi stocks: the total absence of kDNA in trypanosomes from both laboratory stocks and naturally infected domestic and wild mammals. Journal of Parasitology, San Diego, v. 86, n. 6, p. 1289-1298, jun. 2000. VODNALA, M. et al. Adenosine kinase mediates high affinity adenosine salvage in Trypanosoma brucei. Journal of Biology Chemistry, Rockville, v.283, p.5380–5388, dez. 2008. WOLKMER, P. et al. Resposta eritropoética de ratos em diferentes graus de parasitemia por Trypanosoma evansi. Ciência Rural, Santa Maria, v.37, n.6, p.1682-1687, dez. 2007. WOLKMER, P. et al. Lipid peroxidation associated with anemia in rats experimentally infected with Trypanosoma evansi. Veterinary Parasitology, Amsterdam, v.165, p.41-46, 2009. WOLKMER, P. et al. Trypanosoma evansi: cholinesterase activity in acutely infected Wistar rats. Experimental Parasitology, Hertfordshire, v.125, p.151–255, 2010. XAUS, J.A. et al. Adenosine inhibits macrophage colony-stimulating factor-dependent proliferation of macrophages through the induction of p27 kip-1 expression. Journal of Immunology, San Diego, v.163, p.4140-4149, dez. 1999. XONG, H.V. et al. A VSG expression site-associated gene confers resistance to human serum in Trypanosoma rhodesiense. Cell, Philadephia, v.95, p.839-846, out. 1998. YADAY SC. Identification and characterization of cysteine proteinases of Trypanosoma evansi. Parasitology Research, Alemanha, PRELO, 2011. YEGUTKIN, G. Nucleotide and nucleoside converting ectoenzymes: important modulators of purinergic signaling cascade. Biochimica et Biophysica Acta, New York, v.1783, p.673-694, set. 2008. ZANETTE, R. A. et al. Ocorrência de Trypanosoma evansi em equinos no município de Cruz Alta, RS, Brasil. Ciência Rural, Santa Maria v.38, n.5, p.1468-1471, out. 2008. ZWEYGARTH, E. et al. Trypanosoma brucei: Diskinetoplasia and loss infectivity after longterm in vitro cultivation. Acta Tropica, Japão, v.48, n. 2, p. 95-99, fev. 1990.
ANEXOS
ANEXO I – Artigo I
121
122
ANEXO II - Artigo II
124
125
126
127
128
129
130
131
ANEXO III – Artigo III
132
133
134
135
